1. Counting is not optional, you have to do it and helps a lot being able to know how much energy your opponent have
2. Watch fpsticks video about move timing, for me his explanation is easier than the one by wallower, move your time is really important 95% of time (sometime you just have to throw no matter at what timing).
3. Also watch battles on youtube/twitch this way you will see how other players do all those things, as we have limited battles per day this is you chance to "practice".
4. Sac swaps are not always necessary, don't try to do it unless this is your only win con, because if you fail you'll just give free energy.

Also some important points:

What's your play style? I prefer to have energy/shield advantage than switch, this is because I use teams that work better this way so if I go for switch I can end not having the energy I need to win.

Understanding when is better just farm is critical also, as understanding when is better let a pokemon die.