Perfect Shots
When trying for a Perfect Shot (where the bar stops within the middle brackets), the longer you allow the shot to charge, the wider the space available for a Perfect Shot. It is best to allow the bar do a complete movement before stopping it for an increased chance of a Perfect Shot.
Shots
Charged shots cause more damage and have a greater chance for a perfect shot. However, using a charged shot is not always the best choice, especially if there is a chance to hit anything but a perfect shot. Usually three rapid shots are better than one charged shot. Also consider the health bar of the enemy tank. If it is close to zero, firing a charged shot is a waste.
Upgrades
There are four stats to upgrade in your tank. Balance everything out before purchasing additional upgrade levels. This is because each particular upgrade will improve a particular stat of your tank while decreasing another one. For example, if you increase Attack, it will decrease the Aiming; if you increase the Defense, you will also increase the Reload Time. Because aiming tends to work well, it should not be a priority to upgrade. The recommended order to upgrade is Armor, Main Gun, Tech, Ammo, Reload, and Aiming; then repeating the order for the next cycle of upgrades.