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)

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 driving posture – the seat is too vertical, causing a closed hip angle (1). The base of the seat is angled back, causing a closed knee angle (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.)