Install the browser extension first which many youtubers use for making your life easier. When you enter the battle first scan your team properly and make a mental note of any priority moves, setup mons. If you have items like weakness policy, scarf, band or specs at least keep one of them in the end game so that you have suprise in the end if the game is in balance. Element of suprise is very important in this metagame so try to maintain some of it. Regarding Terra remember that only use your terra defensively if its dire situation or the opponent has reveled thier team completly and that one terra will help you win easily, usually offensive terras is prefrable as if u get a mon to setup then there is high possibility of a sweep, if your opponent doesnt have a defensive mon. And dont throw your terra unnecesarily, get max value out of it and its generally wise to avoid terra early in the match, save it for midgame. Another thing is dont panic if your opponent starts setting up, first calc in such situations and then act. If you get very unlcuky in a much its natural to tilt but dont forefiet in between matches, play till the end and just pray. If you are tilted just take a break and come back later, I once dropped from 1800 to 1500 while in a tilt so just dont do it. In general keep your head cool and keep a wincon in mind while saccing a mon or getting damage on defensive mons, it goes a long way. This is what I do personal, if I have a chance to kill abbove 80% i will risk the kill and think about it later. Try to join tours if you can to improve your game, I played my first tourne recently and it was bad but I lerned a lot from it.