Only buy or fill up your car or bike in the early morning when the ground temperature is still cold. Remember that all service stations have their storage tanks buried below ground. The colder the ground the more dense the fuel, when it gets warmer petrol expands. So, buying in the afternoon or in the evening, your litre is not exactly a litre. In the petroleum business, the specific gravity and the temperature play an important role. 1 degree rise in temperature is a big deal for this business. But the service stations do not have temperature compensation at the pumps.
Another most important tip is to fill up when your tank is HALF FULL. The reason for this is, the more fuel you have in your tank the less is the air occupying its empty space. Petrol evaporates faster than you can imagine.
Another useful information is to avoid filling up if there is a fuel truck pumping into the storage tanks when you stop to buy. Most likely the petrol/diesel is being stirred up as the fuel is being delivered, and you might pick up some of the dirt that normally settles on the bottom.
Hope this will help you get the most value for your money.