coo coo... heh, i know it's a hell of a lot easier said than done... but a couple pointers..
1. make it convoluted as hell... like twisty and stuff... kinda like a natural track-ish thing... do you play GT3? a VERY cool track would be tahiti maze...
2. bigger is better.
3. hmm well it depends on what kind bit you are running, but slopes, bumps, hills, and short (but more or less extreme) piles of dirt would help with the realism... the only thing that you have to be sure of is that you are running a bit/clone that can take hills and stuff... i suggest rally racers... or shens...
4. try... well, if u have a lot of playdough from when u were a kid, try that
oh, and check out p-walks track.. or the admiral's snowy track.. that thing looks....so....real...