[Mossy Toes]

Try to find a detailed tactics guide with breakdowns for every units in the codex.

You called? (I shamelessly say, flaunting my only slightly outdated tactica...)

Squire has some good advice when it comes to building combat-leaning lists: having a method of getting there is as important as being able to kill what's there when you arrive. There are lots of shooty armies that will splatter infantry trying to walk up an open field...

Beyond that, experiment! Perhaps proxy things for a game to test them out, if your local gaming store lets you. Try to figure out what legion or chaos god or warband you like the look of...