In order to work out how much solder to use to avoid dripping while soldering, you need to measure the material you are joining with the solder itself. If for example you are soldering a pipe, the amount of solder you should use should be equal to the circumference of the pipe. The amount of solder wrapped around the pipe is the exact amount needed to be heated with the soldering iron.
It is highly recommend that you measure out the exact length of the joint you are going to make, to avoid excess drips of solder being left on the material. Another way this can be avoided is to use a cleaning paste or flux, which together with the heat of the solder will help it to adhere to the bonding surface.