When I was done with the tutorials, I was left with a very simple and generic AI that was probably very similar to whate everyone else had when they reached that point, and it consisted of 3-5 main 'parts' (depending on how you categorize): 1. attack, 2. evade, 3. score, 4.(3b?) catch resource, 5.(2b?,1b?) movement.
From that point, I basically watched battles for ways to improve any one of those 'parts' and soon I had the workings of several small subroutines, and I reached that point just in time for the subroutines update to the game, so I converted them all to subroutines at that point. In my case, there were 4: Score, Evade, Attack, Catch. All movement was split between them.
After that, I watched games for very specific tactics, strategies, weaknesses in my own AIs, weaknesses and strengths in enemy AIs, etc., and each time I saw one, I build a small and simple subroutine to try and mimic any benefits I identified. Then I'd compare those new ones to my "big 4" and see if they fit nicely in to any of them, and I did that using these methods (in order of my priority):
1. directly modify one of the 'big 4' subroutines
2. add the new subroutine as a 'sub-subroutine' to one of the 'big 4'
3. add it as a new 'primary' subroutine (go from 'big 4' to 'big 5' without altering any of the original 4)
4. break an existing 'big 4' in to multiple pieces to accomplish the goal (go from 'big 4' to 'big 5' but completely destroying one of them and replacing it with 2 new and unique ones)
5. combine existing routines (go from 'big 5' back to 'big 4')
6. reorder the existing subroutines or sub-subroutines
7. create an entirely new main AI, with it's own 'big 4' plus the new concept subroutine
8. scrap the new idea
At this point, I have 4 main AIs, one of them has a 'big 3', two have a 'big 4', and one has 'big 5' subroutines. Of all the 'big' subroutines, two of them are common across all main AIs, one is used on 3 out of 4 main AIs, one is used on 2 of the main AIs, and 3 of them are unique to their main AI. There are a total of only 7 'big' subroutines.
I have no sub-subroutines currently in use in any of my main AIs or any of those 7 'big' subroutines, but I have 8 of them currently in testing for consideration.