I have always used two types of AI's
The first relies on a search, you come up with a way of evaluating the current situation to produce a score and then run through all possible moves looking for the best.
The best example of this is a alpha beta minimax search.
The second is a layered approach.
You have a top layer that makes strategic decisions, a middle layer that handles planning a way to achieve the strategic aims, and a lower layer that actually handles the actions.
So the top layer says .. "I want to go to the top of that hill"
The middle layer says .. "This is the route I want to take"
The lower layer moves the character along the route and reacts to local events.
Each layer has a set of inputs.
The strategic layer knows about the overall game state, uses things like influence maps to decide what to do.
The middle layer uses things like A* to plan movement, and terrain scanners to work out in detail where to go
The bottom layer takes game events like "you have been shot at" and can override the other layers, passing messages up the stack when events happen.
What might be a good thing for you to start with is writing your own influence map code, your own terrain scanners, A* etc. and then playing with them.
You will be suprised what can happen and where the code can lead.
After all Lemmings started out as a test for graphic artists to see how small they could get a sprite and still animate it.