ride it!
decide what you want to change/where to put jumps, berms, etc. and improve it as you go
No, not a very good idea.
Find your starting place, ideally the top of the hill.
Leave your tools at the desired spot.
Walk the hill finding all the natural features.
Have a think about where you would like it to go, sit down if needed.
Have a packet of crisps.
With a rake, mark the next 20 metres that needs clearing/building.
Make sure you have a start so that you have speed, ie a bank, or a straight to pedal...
Just go from there really. Just every so often, re-walk the next section to know exactly where you wanna go.
If the wood is open, and not heavily populated, use logs and create switchbacks (so you have to go inbetween, and can't cut) and some jumps.
I've got am awesome track coming along at the moment, i love it, as i'm choosing where its going, and what features are going in, and stood directing it. Oh the wonders of a broken arm!
End of August i'll have some video footage up.
James