Push your passenger seat as far back as possible
If you're in the passenger's seat, which is generally a better idea - and people will tend to offer to drive for you once you're heavily pregnant, just as you'll (hopefully) get offered seats on public transport - push it back as far as possible from the dash.
Position your seatbelt correctly
Remarkably, there are half a dozen seemingly civilised and intelligent countries - including Italy, Greece and even Japan - that provide seatbelt exemptions for heavily pregnant women, seemingly because they think it's safer.
Expert advice, research and plain common sense all agree, however, that it's far safer for you and your unborn child to be restrained in the vehicle in the case of a crash, rather than flying through the windscreen or colliding with the steering wheel at full force.
When driving you'll obviously need to reach the pedals, but try to keep at least 20cm between your body and the rim of the steering wheel. Also tilt it up, toward your face and away from your body.
Positioning the seatbelt is the biggest issue, of course, and it's absolutely vital to keep the lap belt below your bump, so fasten it across your pelvis and upper thighs. If it's around your belly button, it's far too high.
Some women, who start to find the sash belt uncomfortable and annoying, unwisely start tucking it under one arm, or even behind their backs, but the consequences of that really don't bear thinking about.
Instead, you should wear the harness over your shoulder and diagonally across between your breasts and pulled to the side of the baby bump.
Avoid long journeys
Generally speaking, long journeys are probably best avoided while pregnant (try not to drive more than six hours a day and take regular breaks to stretch your legs) as they will be uncomfortable and swelling in your ankles and feet can quickly become an issue, as it soon does on a daily basis anyway when you're expecting.