questions about my KTM 250 smoker

First of all, don't lower your front forks to make the bike sit lower. The hight adjustment will be minimal before you drastically affect the bikes handling. Lowering your forks will cause headshake if you go too far. Nothing wrong will lowering them a little as it will make it turn easier. 4-6mm is probably the most I'd raise them.
Here are some set up tips for you to start with.
http://www.motocross-racing-tips.com/dirt_bike_suspension.html
If you don't want to do it this way, I would suggest you leave it stock for now.
As far as ruts, just look ahead and don't think about them. Your bike will go where you're looking a lot better than you think. If you're looking at the rut, you're gonna fight it and lose.

And for the re-valving question, this doesn't apply to two strokes. You are riding a smoker, right?

You need to decide before you enter the turn whether or not you're going to ride the rut or flat track. If you ride outside of the rut, I recommend you go practice on your flat track. You need to sit forward on the seat, over the gas tank. Push on the outside foot peg, and let that rear wheel slide. This will get you around outside of the rut. If you settle in to the rut, you need to keep your speed slow enough so you don't pop out of the rut. I like to lean back a little to get the weight over the rear wheel while in the rut or berm.