Firstly, Asking the question "How do you Mod?" brings up a lot of different replies and more professional users would reply with "Check out the Modding Tutorials on the Site" Well, Let me tell you that the Modding Tutorials can't teach me how to make A.I.s now, do they? So, i need your help. I've been planning this for quite a while and have actually done the base pixels for it already, but to tell the truth, i don't know HOW to make A.I.s and that's where this thread comes in...
I'm sure people have suggested taking existing assets, looking at them and optionally modifying them in a dozen of other threads, but here it is again. Unpack the assets, and check out the ../ai/ folder. By looking at the structure and content of these files you should be able to figure out what each file does. I suggest you first make a mod that modifies an existing AI, before making a new one. If you don't understand the syntax, that's the same regardless of what you're trying to mod. Guides such as http://community.playstarbound.com/resources/unofficial-modding-ebook.2930/ will help you with that (and more). Starting small is also recommended. Following a guide for something you don't necessarily need (such as creating a weapon, there's lots of guides for that) may not seem helpful but it will make doing something more advanced a lot easier. Information on various file types related to AI: http://starbounder.org/Modding:Ai.config http://starbounder.org/Data:Assets/frames http://starbounder.org/Modding:.aicommand http://starbounder.org/Modding:.aimission Edit: also, http://community.playstarbound.com/threads/custom-ai.89163/.