[TSM330i]

Definately get used to sitting straight up with your backside against the back of the seat. Get the seat adjusted as low as you possibly can in the car, but are still able to see clearly. I'm 6'1" and have a longer torso so with the stock seats, I don't feel I'm low enough.
Remember also, your shoulder blade should be touching the seatback with your wrist being about to touch the top of the steering wheel at the same time. Adjust the wheel in or out to do this while being able to touch the pedals properly.

This position allows you to react quickly and keep the car in control. It's one of the first things the high performance driving schools will teach. If you're not seated properly, your first reaction is to move yourself forward in order to react to anything that comes up in front of you (i.e. avoiding something).
That reaction to get into the proper position is wasted time and you may hit whatever you're trying to avoid.