Both the Bacteria Starting Power and Bacteria Power Per Turn are added up to determine the initial Bacteria Power. In our example this amounts to 65.
Ending the turn will first reduce every tile's strength by 1, except for resistant bacteria. In our example 29 tiles lose 1 strength, bringing us down to a total of 36.
Next all isolated tiles die off. In our example that's three tiles near the top for 1+2+1= 4 strength, bringing us down to 32. Note that the third isolated tile also gives us a bonus dose.
Now the important part happens: First the remaining bacteria duplicate for +32. Then the Bacteria Power Per Turn value is added for +15, bringing us to a total of +47. This number is then added to the board, passing the turn back to the player, who is now facing 79 Bacteria Strength at the start of turn 2.

The doubling of the remaining bacteria is somehow not mentioned in any of the tutorials, but is the major contributor to danger. It is vital to understand how this mechanic leads to exponential growth. Having few bacteria on the board will slow down growth to a crawl while having (only) half the board filled with bacteria usually means game over the next turn. Having a few 10-strength tiles around can make Bacterial Growth surprisingly strong.

Which specific tiles will get how many bacteria is entirely determined by (weighted) randomness. Unfortunately there is no way to predict bacteria spread. The game however seems to be kind enough to refrain from randomly filling up the board, because as soon as bacteria spreads to the last free tile, it's game over, even if all bacteria would fit.

The scoring is pretty simple and fully explained in the Stars Tutorial. But to have it all in one place, let's review the scoring rules:

• You get 10 score per point of damage from any source. This encompasses both damage from manual dosing and from the automatic -1 to every tile at the end of a turn.
  
• Damage score points are doubled for any bacteria which die off due to isolation. If you isolate a tile with 7 strength, it'll lose 1 strength for 10 and then give you 120 points as it dies.
  
• Lastly, any dose you have left over at the end of a level will grant 100 bonus points.

The game does not reward finishing early. In fact each missed turn will put you at a significant score disadvantage, since you miss out on additonal doses and additional kills. You should always strive to go down to "turns left 0". Note: After hitting "end turn" you will still get a bacteria phase with a gobal -1 and isolated tiles dying off. But then the board must be empty, or you lose the game.
Take-away: Drag your games out for as long as possible.

Your first order of business is getting ahead of bacterial growth. This can be done either by killing off enough bacteria so their growth is sufficiently curbed, or by researching to a point where your saved-up doses have enough killing-power to handle their numbers.
The second goal is to now farm points. Growth can easily get out of hand, so you should approach the desired level of the Bacterial Strength slowly and carefully. Once reached it is important to kill about as many bacteria each turn as will regrow. Looking at the handy graph in the top right corner, this produces a recognizable sideways zig-zag pattern. Looking at the graph you can also easily spot deviations - where you've killed too many or too few bacteria last turn - and correct them. Towards the end of the level you'll want to slowly reduce bacteria population just to be on the safe side.
Take-away: Any successful strategy aims to reach a stable equilibrium between growth and points harvesting.

Your research strategy will depend heavily on the parameters of the level. A few general points though: Try to not narrowly miss research goals - nothing worse than ending a turn with 39/40 and getting overwhelmed the next turn. If Antibiotic Power 2 is in reach, it is almost always a good idea to save up most if not all of your doses. They will literally double in strength the next turn and you would be wasting power using them now. While highscoring, you will often deal with high-strength tiles. This puts particular emphasis on Antibiotic Powers 3 and 5 as they allow you to kill 10-strength tiles in 3 or 2 doses respectively. Lastly, high levels of research mean you have to spend fewer doses, which means you can expect to get more bonus points of left-over doses.
Take-away: Research whenever you can. Antibiotic Levels 2 and 3 are huge increases in power and invaluable tools on every level.

Every third isolation in a single turn will net you a bonus dose. These are a very powerful tool. At worst they give you 100 bonus points at the end of the game. At best they make the difference between survival and game over.
Isolations may not always be the best scoring strategy, but if you do isolate tiles you should always try to do it in multiples of 3. Since there is no carry-over between turns, isolating 2 tiles first and 1 tile the next turn is just wasting the bonus dose. If you can find a third isolation at the cost of a single dose, you are essentially looking at free points, since you'll get the dose back.
Take-away: Try to isolate multiples of 3 each turn.

Clearing tiles does not have any inherent strategic value. Growth is determined by Bacterial Strength, not by the number of tiles. What is determined by the number of tiles, is the automatic -1 strength at the end of each turn. On a board of 25 tiles, having 10 4-strength tiles may seem cleaner or at least equivalent to having 20 2-strength tiles, but the latter is the stronger position by far. You will get 20 free kills and thus 200 points at the end of the turn compared to 10 or 100 points. On a spread-out board it is also easier to create isolations than when bacteria are clumped up. Yes, the board will grow much slower, but on the flipside you will save doses which can partly cancel out the score loss.
Not putting a focus on clearing tiles is especially important early on, when you are still trying to overcome bacteria growth. Let's look at an example where you are close to losing and have 1 dose left at strength 4:
It might be tempting to isolate the 9 and clear 4 tiles in the process. But (accounting for the -1 you'd get at the end of the turn anyway) this will only decrease Bacteria Strength by 4+4+3+8= 19, while clicking anywhere into the big patch will decrease bacteria strength by 7*4= 28. Those 9 additional bacteria spawning might make the difference! And even score wise the isolation only brings you up to 230 points, compared to 280 points for the left option.
Take-away: Clearing tiles is not always the best strategy. Often Bacterial Strength is a much more important number to control.

Since each left-over dose will net you 100 bonus points at the end of the game, this may act as a baseline for dosing decisions. Still, it's hard to put a number to a dose, since it may benefit you down the line through slowed bacteria growth, isolation bonus points or bonus doses. I still strugle with this calculation myself, but I find the concept helpful in extreme cases where the board ends up in an unlucky state where I would have to dose a single 2-strength tile to get a 2-strenght isolation. If you are not already looking for a third isolation and the dose is practically "for free", it's always worth looking for better uses for your dose and maybe returning to the area next turn.
Take-away: Doses are valuable. Try to use them only when the outcome is a net-benefit.

Broadly speaking there are two types of levels: Most will allow you to invest a large part of your early doses into research, making you more powerful while you wait for bacteria to grow, before the harvest begins. On these levels early aggression will simply reduce the number of points you can harvest later on.
A select few levels with high Bacteria Starting Power and slow research ("Dry on Doses" and "Reduced Research" come to mind) will not afford you that luxury and force you to adapt instead. On these levels early research is a trap, because you will not be able to catch up to bacterial growth. Instead beat them down on turn 1 and then save up for research. Due to exponential growth it will take them several turns just to reach initial starting levels and by then you will be ahead because of research. Just be careful to leave enough survivors as to not impact your score harvesting later on.
Take-away: Early aggression is generally bad for your score, but may be necessary if research is slow and bacteria are plenty.

Since the bacteria distribution is randomized, luck can make a big difference in survival and especially in highscoring. To showcase the impact, let's look at turn 1 from Bonus 4 level:
In the first layout you cannot isolate any bacteria even expending 2 doses. Ending the turn will cause a natural decrease of 13. On the second layout 1 tile is naturally isolated and expending a single dose can isolate 2 more. The bigger number of tiles amounts to a total natural decrease of 20. Expending the single dose will decrease Bacteria Power by an additional 9 and also net you a bonus dose. On such a very hard map starting with 80 Bacteria Power, it makes a huge difference whether 13 or 29 die off at no cost in the first turn.
Take-away: If you get a bad initial setup, no shame in rerolling for better starting conditions.

Here are two basic strategies that I've found to work quite well. They are simply derived from the analysis above, so you can probably come up with your own at this point. Note: On levels with whacky parameters you will still have to adjust your approach.

This is my go-to general purpose strategy. Start by picking off easy opportunities at isolations (always in multiples of 3 of course) and by generally saving about half your doses for research. Start concentrating your efforts on one half of the board, while leaving the other mostly untouched. In the end you want to have about 1/3 of the board filled with 10s, which will act as a reservoir for growth. On the remaining 2/3 you want to set up as many isolations as possible. Keep in mind that isolations double points, so keeping the isolated tiles at high strengths is very beneficial.
This strategy makes you spend a lot of doses, since isolations will often require you to dose just 1 or 2 low-value tiles. While you will also gain a lot more doses through triple isolations, you will generally not have a huge reserve left over at the end of the game. Thankfully you will gain more and earlier points through isolations to compensate. If you see that you're running low on doses, it may be prudent to slowly tear into your reservoir about 2 turns before the end, so the population becomes more managable for the final clear.

This is a totally different approach that can be fun to try, but won't work on every level, as you need a decent supply of doses so the sheer amount of bacteria you'll be handling won't overwhelm you. We don't care about tiles or isolations. All we do is harvesting as many bacteria as possible with as few doses as possible.
Let bacteria spread until the board is somewhat evenly filled with high-strength tiles. Then you evenly dose them down to 5. The end of turn will bring them down to 4 which is safely below half of the board. The growth phase will then fill you up to 9s and 10s again. Rinse and repeat.
This is a somewhat basic and surprisingly stable strategy that still produces great results. Since you make the most of every dose, you will save up more than with the first strategy, putting you well ahead in terms of research. Unfortunately this is also where the strategy starts to break down ultimately. Once you reach high Antibiotic levels you cannot evenly dose everything anymore, since it would tank your population too much. Still, since almost every tile will be covered at the end of turn, you get lots of points for free via the -1 mechanic. And since you'll have left dozens of additional doses, you will catch up on the final screen as well.
When finally clearing the board on the last turn there is of course no reason not to also go for isolations.

I think the first strategy is generally stronger, but with the high degree of luck and randomness in the game it's honestly hard to tell.

Happy dosing!