You need to wrap the tape so that when the fitting screws in it tights, not undoes the tape. On a standard right hand thread this means going clockwise around the thread. Another, lesser known trick is to feed the roll of tape in such a way that you can maintain even tension. If you look at the above picture you can see that the roll is away from the pipe. This means that I can ensure there is enough tension on there to pull the tape down into the threads and make for a good seal.
I usually do 2 or 3 wraps, but this depends on the depth and sharpness of the threads. Putting too much on will make it hard to screw the fitting together and can cause bits to be cut off and carried into the flow. To finish applying the tape I just pull quite hard on the tape while keeping it as if I just wanted to increase the tension of the wraps. This will stretch the tape until it tears and will leave it nice and neat.
If you find that you've wound the tape the wrong way when you start to screw the fitting together then simply unwind the tape and start again in the other direction.
I hope you find this useful at some point and if you've got any other ideas on how to apply plumbing tape please share below in the comments.