SiMPLE | Forum

There is nothing easy you can do to get better except practice. A video won't help. Some of the people you play against may have MANY years of practice. Hundreds if not thousands of hours.
You may want to try single player mode and play through all the maps...MANY times.
Aim where the opponent will be, not at where they are. Aim and fire slightly ahead of their direction of travel. But all that depends on their angle of movement relative to yours, your ping, their speed of travel and your speed of travel. Every encounter is different. Oh and don't stand still for more than a second or two. Keep playing and practising and eventually you will get better. But don't expect this to happen quickly.
You will die more times than you kill.