Ideas For Track
I've got some pics of my backyard track on my website:
http://my.voyager.net/aaronsmith. Follow the link to "Backyard MX." The files are huge, so go grab a Red Bull while they download.
In Michigan, the biggest deal is setting up your track so it drains after the rains. Othewise you've got big puddles, and by the time they dry up, the rest of the track is bone dry and rock hard. This may not be a problem in your locale, however.
Set up your track so it won't be a one-liner. This will keep you from getting bored so easily and will make you a better rider. Ideally, you can set-up your track so it can be run both directions (Jeff Stanton has a good one). The only problem is that the jumps will be do-or-die, and you will need a way to groom the turns when you change directions (the same corner taken as a lefty vs a righty develops vastly different lines). I set my track up to run mainly one direction, but I can run it backwards for fun sometimes. I also set up the jumps on adjacent straights so I could play ride and hit them sideways, diagonal, etc.
Most of all, make it challenging yet safe. If you get hurt practicing on a peaked 8 foot high double, you won't even make it to the racetrack. Save the heroics for the races!
Have fun!