Shift gears around 3,000 RPM on the tachometer as a safe practice for smooth shifting and better fuel economy. With practice, signals for shifting gears would be when you hear or feel the car is reaching a high rev on its current gear.
On busy streets or a congested neighborhood, many drivers tend to find second gear and maintain it through traffic. Second gear offers just enough power to keep the vehicle accelerated enough to get through a busy city street or even up a steep hill in slick conditions.
Shift gears when you feel that the car has reached its maximum revolution for that gear, which is usually between 3,000 and 4,000 RPM. For faster acceleration, prolong the shifting towards 5,000 RPM to make the car produce a quicker revolution and add a significant boost into the next gear.