Ya gotta pretty much drive to go anywhere decent....
There is always Shady Grove out by TX Stadium. It is a practice MX track that is awesome - that is if your definition of awesome includes the terms "hardpack" and "dusty" :)
If your definition of awesome includes the above terms, then you will also like Boondoxxx out by Lake Lavon. It has a kids "track", a peewee "track", a MX "track", and some trails too.
Oh - there is a little bit of sand out at Muenster too, or so I hear. :laugh:
Muenster is truly awesome though.
Try Rocky Ridge for starters - it is closer than Muenster and not as sandy with lots of open area for practicing basic skills.