There is a few things you must understand before you step on the pedal and finish on last place in the single-player campaign .

There are a few tricks besides moving the wheel left & right, and thrusting the accelerator up/down and abusing the brakes.

For example, there are N-ways to brake and bring your car to either a full-stop or speed reduction:

1st - Use the Normal Brake
Besides stepping on the brake pedal, You can also tune how the brake works in the tune options of your vehichle.

2nd - The Handbrake
The handbrake is a well known form of brake, mostly used for drifting around in other games, i'll add up more to this section later. Note that this can also be tuned.

3rd - The Engine BRAKE
That's right, you've heard it right: The Engine BRAKE

Did you know that you could use your car's engine to bring it to a complete stop? Yes, you can! No, it's not by turning it off, 'cus you can't do that in Dirt Rally, but you can & should definitively use your gearbox to bring your car to a halt, specially in those situations you would most likely have completely lost control of your car if you stepped on the brake pedals; in order to do that, all you have to do is shift down on your gearbox, let's say you're 80Mph at 4th gear, so by simply bringing your car to 2nd, it should be enought to bring your car's engine down by brute force; ofc, this should damage your car's engine a bit, but it's a complete safe alternative way of braking your car in a video game. Not only it's safe, it's also better, because it also keeps your car completely stable on the road in situations where using the normal brake or the handbrake would completely throw your car out of it.

This mechanic exists in pretty much every other racing game, because of how the nature of the gearbox system works: the lower your gearbox, the lower your speed!

Surprisingly this technique also works in real life too! Except that you'd really have to pay for all the damage done to your own car in a few months from abusing this.

How to improve a car's stability / Help my car doesn't keep on track!
Access the tune service - if you're on career mode, you'll need to buy that car's upgrade that gives you access to the tune service - and once you've done that, try changing all property/attributes that give you + or - stability: change them all to more stability.

That's it, welcome to Dirt Rally 2.0. Note that this also fixes the porsche DLC car's handling not being very stable which a lot of people on the reviews are complainning. :^)
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Summary:
So this is it for now, I'll bring more tips as more users talk about 'em in here(or not); either that or if I find anything new on my own.

1 - ALIGNMENT
There are two things to check here, Toe Angles and Camber Angle:
Negative Camber Angle improves cornering grip, that means your car has lesser chances of losing control while doing curves. But Negative Camber will make you more likely to lose control of your car in straight-line roads.

IMHO, A Negative Camber is what you want in your car, but don't add too much negative points or you'll start losing control on straight-line action which means you'll have to drop gears down and acceleration down a lot in order to not lose your car.

As for Toe Angle, you can either Toe In or Toe Out by giving more or less points to either of each. In this case, you should always Toe In the wheels on your vehichle because that'll give you more stability, and this is what you're looking for in a Rally Game, because you don't really want to lose control of your car in a 15~20mins race.

This Alignment tip is pretty much benefitial to every single car available in the game, but you need to set them manually to each and every car you own.

2 - BRAKES
Braking Force dictates the strength to reduce your car's speed to a halt.
The higher the braking forces, the higher chances it has of locking wheels,
A locked wheel can cause the vehichle to overturn on both straight-line action and at cornering, so adding or removing points here will totally depend on your braking style.

For example, Personally, I don't like stepping down on the brakes for long periods of time, instead I prefer shorter periods of times pressing the brakes more than once to stop the car, so in this case I always add to Braking Force.

But I reckon that some other people might prefer stepping down smoothly on the brakes, instead of pressing it many times. So in this case you might prefer lower braking forces.

Both require totally different braking techniques, it really depends on how well you
perform at one or the other. It's a personal choice.

Brake Bias decides whether to brake at the front of the back of the car. Again, depends on driving style, I always add mine to 80% front as I'm always speeding down right before the corners.

Regarding these 2 options, you should try different settings and see which one better fits your driving/speeding/braking style.

3 - DIFFERENTIAL
LSD Driving Lock: a high lock profile will improve straight-line action,
but may induce oversteer on low grip conditions. a low lock profile will improve cornering at the cost of straight-line action.

LSD Braking Lock: a high lock profile here will improve traction under braking
at the cost of understeer on cornering. A low lock profile will improve traction on cornering conditions but will compromise straight-line action.

LSD Preload: a high profile Improves on corner traction, but setting it too high compromises straight-line action by causing steering.

Personally, i don't usually mess with these, but if you feel like your car is getting
out of hand too often on certain tracks, you can try meddling with these.

4 - GEARING
This should be simple, shorter gears improves your torque, at the cost of lower top speeds while longer gears improve on top speed at the cost of torque.

Some cars like the porsche can benefit from these settings, for example, you could try setting the 1st gear to LONG a little bit, because the Porsche already has too much torque, which can often cause you do understeer or understeer.

Cars like the Subaru have a lot of Top Speed and little Torque. The Final Drive option is there just in case you don't want to meddle with all the 6th gears at once, the purpose is the same.

5 - DAMPING
This is where the fun starts, the DAMPINGS dictactes when the SPRINGS are going to activate. While the SPRINGS decide how your car is gonna react to road crumbles.

Usually, the more firm your bumps the greater the Stability, but adding too much FIRM bumps can compromise driving on off-road crumbly conditions - Like Argentine Offroad roads for example.

everything in here should be set to +3.00 FIRM, unless you want more SPRING response.
save for the BUMP ZONE DIVISION option. This should be set to Default. It's the one that has Slow & Fast as settings instead of Soft & Firm. Leave this one to default.

6 - SPRINGS
Finally, Low Ride Height improves overall stability, but makes SPRING response
more difficult, lower your Ride Height if your driving conditions don't really need too much SPRING response. - Driving in Argentine might demand more spring response, for example.

Spring Rate dictates how your car is going to absorb all of the bumps in crumbly roads like argentine, setting it to FIRM will increase your Car's Stability, but will reduce traction and stability under Crumbly Conditions(yes, you figured it out: like argentine). A FIRM settings will make your car jump more often, therefore making you lose traction and stability on those conditions.

Leave Anti-Roll bar to it's default settings. Don't bother with it.


-- SUMMARY --
This is pretty much it. The Alignmen Settings given in here are pretty much Global to every vehichle in this game, but you need to set them manually according.

The Braking Settings will totally depend on your braking/cornering/driving style

Spring and Dampings depends on the Road's Condition.

Gearing settings depends on how much Torque/Top Speed the car already has by default.
If it has too much top speed, like the Subarus do, then you should set the Final Drive to shorter. If it has too much Torque - like the porsche does - then set the Final Drive to Longer. Too much Torque will cause understeer/oversteer right at the 1st gears. Too much Top Speed will make Corner & Braking Recover a lot more difficult. The settings on these depends on what the car is already capable or not capable of doing so - like what the Porsche can for example.

Differential Settings depends on how well you're doing with your own current overall settings.

------ ABOUT ---------

The reason I wrote this guide is because I saw a lot of people complainning on release day that they couldn't drive X or Y car, because it keeps drifting away from their hands(like the porsche!).

Plus, you can get a lot more stability from all the other settings as well, for both normal and offroad conditions and snowy conditions.

Another Hint:
And if you really feel bad about changing the gearboxes at all, you can just gear up to 3rd gear if you feel your car is gonna drift away after trying to recover from a instant brake or a corner. This tip is really useful at snow stages, just gear up to 3rd instead of 1st gear when recovering from brakes and corners.

Picking which tyre you're gonna use is just as important as tuning your car. You'll usually be given a choice before the first 2 stages and right after the first 2 stages to pick a tyre type. You should pick your tyre type according to how long those first 2 stages are(or how long the other 2 following stages are).

IMHO, you should always pick soft tyre for the 1st 2 stages of an event, because even if it wears off due to distance, it's still daylight and driving isn't as difficult. As the day turns into night and the 2 last stages come, you might desire to pick medium tyres, because driving is gonna be more difficult and having your car sliding around because of tyre wearing off is gonna real be a pain.

BUT should you feel that the last 2 stages have a short distance, you can always pick Soft Tyre. Tuning your car for more stability at this point isn't going to save you when the tyre wears off on the last stage considering you will also have lower visibility, so be warned.

Always keep an eye on TIME, WEATHER and DISTANCE conditions. Long Distances mean your tyres will wear off for the following stage, and if the following stage is also another long one, that means trouble. TIME impacts on visibility, the less stable your car becomes the more impact it will suffer from visibility conditions. Bad Weather like rain and snow will directly impact your car's performance so having a wrong settings like a worn out tyre will make it even worse.

You should tune differentials so it's not high too much, because it'll cause understeering AND it's not so low to the point you're not getting any benefit from it.

The better your acceleration is, the faster you'll come out of curves and drifts, but the harder it is to handle your car on a keyboard. So if you're a keyboard player, like myself, you might want to add up top speed instead of acceleration.

Furtherover, some cars have so much acceleration it's hard to control it during curves and drifts, so increasing top speed will also fix the issue.

You know whenever your co-driver/co-pilot says 3-left, 4-right and then the sign appears on screen, those numbers means more or less which gear your car should be in during a curve.

If your car only has 5 gears and he says 6-left, that's likely you can use top speed on gear 5 to take the most advantage of the moment. Of course, this depends on your gearbox tune settings, if you've put too much top speed, the rules of the game may change here, 'cus having too much top speed means you could be on gear 4 and running just like gear 6, same if your co-pilot asks 2-left you might just have to go down to gear 1 instead if you have too much top speed.

Furtherover, having too much acceleration(in the gearbox tune/settings ) as opposed to the stated above means you'd have to increase the gear from gear-2 to gear-3 or gear-4 depending on how your settings are for the gearbox.

Knowing this helps a lot with the racing in this game specially in night stages or rainy sessions. Knowing that your tyres are damaged from a previous race and that 4-left might mean gear-2 and not gear-4 helps a bunch!

Last but not least, when your co-pilot says 6-left you should pay attention if they give extra details as in "6-left short" or "4-left sudden" because even if they appear like easy drifts, being a 'short' or 'sudden' would make the drift much more difficult. Your co-pilot can also talk about bridges or wood/logs and also stones and crests, so coming out of a gear-6 into a bridge or wood/logs is dangerous, because it's too fast to adjust your car and you should becareful in order to not lose the race. Playing on realistic difficulty and making a mistake on any of these will cost you your entire car along with all it's upgrades.