Alrighty then, check me if I am wrong, the YZ250 is all stock including gearing, and this is your first dirt bike?

If this is accurate I wish you luck
Is it jetted for altitude or city? You will probably want to look into a weighted flywheel for that beast and drop your counter sprocket -1.
If you are really familiar with riding a 2 stroke MXer you might be able to fore-go these mods for awhile, but you will find it to be a handful on the technical stuff. Keep looking in this forum and there will be some rides but as this is predominately sportbike forum you will have better luck on Thumper Talk in the Rocky Mnt. Region.
http://www.thumpertalk.com/forum/forumdisplay.php?f=59

I am headed to Utah for a Supermoto Race this weekend but possibly next weekend. Can you ride during the week? Much better at Rampart to avoid weekends 'till late season.