Rule of thumb on POSITIONING
Since the fighting is carried out automatically, you might forget that you do influence the outcome in Teamfight Tactics beyond simply assigning items to your Champions. You need to remember that where you place each Champion can make all the difference. As a rule of thumb, you wanna place your assassin in the back line and they will teleport automatically to the enemy's backline at the beginning of the match. Usually, Assassins will leap straight forward so your opponent may shift their units around to change their course to prevent you from killing their Champion. Since your opponent team is random, it's hard to anticipate. Stay alert and keep an eye out to predict what they are upto and react accordingly. Another general rule is to place high damage but weak classes like Archers and Sorcerers behind tougher and tank classes like a Guardian or a Knight.