If your car has an RPM meter than do the following:
- When you are driving normally and not pushing the car, shift every gear when you reach 3 RPM the next gear will start from 2+ RMP power.
- When you are driving with a bit of a power then it is better to shift the gear after 4+ RPM, the car will be in power all the way.
- When you are pushing the car, shift the gear before RPM needle reaches the RED area (In most cars that area start around 6 RPM)
when it comes to no RPM meter, 70 km/h for normal, 80 to 90 km/h for power, and when pushing you can change around 120+ km/h of speed.
Hope I answered your question.