Assume everything you do and see is a second behind what is actually on the screen. If 2 people are running and they are behind you, then they are actually next to you most likely. When you shield and get barraged by attacks, those attacks where already registered before your shield, etc... you basically have to anticipate instead of react to most things in PVP. Feel when crowd control is coming and pre-purify. Know when bursts are going to happen and pre-shield. You get a feeling for it over time.