The basic items you need against AIs in your loadout should include:
-Money maker
-Power generator
-Bucky
-Armadillo
-Ratchet
-Arty/Archy(optional)

The remaining slots in your loadout, you can place anything you want.

Why the loadout?
Money Maker
The staple of every game, online or offline. Moneymakers do what they do best, generating credits that you have to use.

Power generator
May not be very neccessary if you are playing with friends or online, but on solo the AI may expend your power on unneccessary geminis, then send them off into suicide haven. Overall try to have this in your loadout, you never know when you are running out of power.

Bucky
Used as your main aggresor against the AI. Buckys have longer range than the T99s and Longhorns that AIs usually place around their bases.

Armadillo
Cheaper than longhorns, does effective with cost and power.

Ratchet
Don't even touch the patcher. Ratchets are way better.

For defences, if the game does not provide you with some starting defences, or your partner does not place any, just buy 2 armadillos and place them in a line in front of your main base door. In some maps there might be a neutral jackal which will drive towards your main base. Just place the tanks where enemies come from. AIs at the start of the game may try to throw one armadillo on your base. Later on they will be too busy fighting your attacking forces to bother about your base,

Money makers and generators should be bought and used on the pads. You can decide how you want to ratio out the two, but do it quick and be ready for game start.

When the game begins, don't even bother to cap the outposts around your base. Unless you are playing on maps that are very small and have neutral barricades that block free passage to enemy outposts.

Buy two armadillos(you should have enough to buy them) and airlift them all the way over to the outpost that is closest to the AI main base. Drop them infront of the outpost and let them do their job.(AIs usually do not have defences around their outposts)

Meanwhile, fly back to base and collect four creeps and drop them to capture the outpost with your armadillos. Have a build queue of armadillos/buckys/ratchets, it is up to you to decide which to produce more of. When the outpost is captured, quickly draw your build queue out of the outpost, and concentrate them infront of the outpost.(AIs will send units from the front, they do not really backstab often)

As a general rule of thumb, it is vital to have at least one or two ratchets.

Now that you have your outpost secured, start collecting your army.
There are two basic types of buildups:

1.Bucky Attack
Start building around four-five or more buckies, the more the merrier. However, you need to also build at least four or five armadillos to protect your buckys. Include two ratchets to repair your units.

When you have a sufficient force, place your units infront of the enemy's base. Make sure that your buckys are actually able to fire on the furthest North T99 of their main base(If you are attacking from top outpost), or the most bottom, if you are attacking from below. Make sure the units are out of the T99 ranges, so they do not get hit. The AI will keep trying to fly over and take on your units, but with you as a personal guard and enough armadillos to fight back, AI attempts will usually foil. Move your units abit forward until you take out the immediate threat(Enemy units that can hit you if you enter from that corner of the map). Do not worry about defences on the other end of the base. As long as you expose one half of the enemy base, it is go-time for your entire force to go on attack mode(Y). It is advisable to put a few units on hold mode, as the AI will try to decimate your attacking force. Protect your units, and soon enough you have your victory.

2.Arty Strike
A variation. About the same as Bucky attack, but this time, you buy four artys and place them outside the enemy base. When placing, shoot with your mouse so you precisely position the artilleries. You then encircle them with armadillos and ratchets. When the Artys decimate the turrets of the enemy base, you can attack however you want.

There are many different ways to destroy AIs effectively. This guide is just a basic guide and there may be faster methods. Of course, it is up to you to discover your best playing style!