Tyre pressure:

If tyres run out of the correct pressure, they lose contact to the road. The lifetime of a the tyre is reduced in such a case, because internal destruction is speeded up. Moreover, fuel consumption rises. That's why it cannot be stated often enough: look after your tyres and check pressure regularly at the filling station. Correct tyre pressure is indispensable. The correct value is stated in the operation manual of your car. You have to take into consideration though, that this value can vary from case to case depending on load, speed, and the type of tyres you are using. If in doubt, ask an expert.
Check tyre pressure regularly every three or four weeks with an emphasis on "regularly". If a lack of pressure is clearly visible, then you have waited too long. Tyre pressure has to be checked in cold condition – after a long drive with high speed the value wouldn't be correct.
Close the valve caps tightly. Replace lost caps immediately, otherwise the valves might become leaky. Check the rubber valves for damages at the valve seat.
Don't forget the spare wheel. This should also be checked regularly, otherwise you might be in for an unpleasant surprise if you have a flat tyre next time. On principle, the spare tyre should have a higher pressure by approx. 0.5 bar above the nominal value.