Three quick tips for good driving posture

Adjust the seat forward or backward so that there is still a slight bend in your knees when you fully depress the pedals.
(This is especially important for the brake pedal.)

Good car seat setup requires an open hip angle (1) and an open knee angle (2)

Good car seat setup requires an open hip angle (1) and a slight bend at the knee  (2)

Adjust the base of the seat to make your hips as level with your knees as possible.
(This might raise your whole body up in the vehicle, and for tall people, this might make you touch the roof. In this case, adjust as much as is sensible.)

Bad car seat posture

Bad driving posture – the back of the seat is too vertical, and the base of the seat is angled back. This reults in a smaller hip angle (1). and raises the knees (2).

Recline the seat backwards a little from vertical. You need to feel that when you relax, your weight is falling back onto the seat and not wanting to fall forwards.
(We often think that sitting ‘upright’ is good for our backs, unfortunately in a vehicle, this can actually make things worse.)