I've been using Grid for years, ever since Molten Core (in fact, one of my first posts on WoW Insider was about Grid), and I still learned things from this article. The way Grid composites information onto its little squares is not intuitively obvious, so it's probably worth taking a look just for that. There is also a video on how to configure the mod, which might give you a hint just how complex it can get. The post ends with a list of some useful plug-ins for Grid; I fully agree with the author that GridStatusThreat, which shows which raid members have aggro, is a must-have (although I can't find a working link to it at the moment – is it included with Grid these days?).
how to configure it.