First of all, in order to draw long straight in shots you must have good fundamentals. If you are not fundamentally sound, then you must see an instructor to fix you up.
Assuming you have proper balance, stroke etc. there are a couple of drills I would suggest.
Watch the draw drill. Try to move the OB a diamond further once you have become better at this.
http://www.youtube.com/watch?v=Ew4cXh6alJU
The control of the draw shot is much more important though, so here is a wicked drill which is very difficult but can help you a LOT. See these 6 spots on the table marked with a cross?
I know I didn't mark them up good, but I think you will understand where these 6 spots really are on the table. These 6 spots represent an imaginary rectangle. Now, take 6 balls, the 1-ball the 2-ball...all of them through the 6-ball. And place each one of them to each spot in a completely random order. Now, you have to run the table in rotation. The rules are simple: The cue ball must
never go outside the rectangle, and each OB must be pocketed to its nearest pocket. (each pocket will receive one ball) This drill will teach you to stun and draw the CB with great control, because if you go outside the rectangle, well, you lose

. Tip: think 3 shots ahead always, like you do in 9-ball.
Be patient with these drills, it takes time to learn how to do them properly.