well, first, try and make some lists up in your head, and try and visualize them on the battlefield. Also, don't say no to a unit just cuz the internet says no to them (except flayed ones, they suck), sometimes they can surprise you.
http://1d4chan.org/wiki/Warhammer_40,000/6th_Edition_Tactics/Necrons thats a good website to look at, its funny so its an easy read, and may igve you some ideas.
Its easier if you can come up with some lists, then people can try and improve on them.