Mistake #1: Over-extending.
If you are constantly getting caught in ganks, you need to increase your overall map awareness. Buy more wards and expect ganks to come. Don’t push out unless you have teammates with you.
Mistake #2: Staying too long.
After winning a fight or objective, don’t wait around for the enemy to regroup and respond. Be aware of when your opponents are coming back by timing their movements. Always overestimate the timing to ensure security. It takes about 6 seconds to get back to the inner towers and 25 seconds to get from the base back to the lane. It’s ok to back!
Mistake #3: Figithing without your whole team.
4 vs 5 rarely works out so play safe and make sure that your whole team is together before you engage or get engaged on. Even if you have to forfeit objectives.
Mistake #4: Taking objectives when you should be elsewhere.
Breaking off from your team, leaving them open for 4 vs 5 attacks, allows the opponent to push for game. If you were fighting all together, your chances at winning would have been a whole lot better. Past 40 minutes, your sole focus should be beating the other team.
Mistake #5: Dying in an attempt to save an objective.
When the enemy team is pushing down a tower, unless you have a ton of aces up your sleeves, they can really just ignore and come out with a kill and the objective. When the opponents are in control and there’s nothing you can do to stop them, you need to realize this and back off.
Mistake #6: Dying in an attempt to save others.
If your teammate gets caught, sorry but you should just let them die. Most of the time, they are a lost cause like the objectives. Two deaths or more are a whole lot worse than just one. By knowing your limits, you have a better chance at winning. If you are the one stuck, send your team back if there’s no chance for you to make it. Dying sucks but at least you saved your teammates from making a grave mistake.
Mistake #7: Diving in when you shouldn’t in teamfights.
Unless you have a team composition based around it, diving in in teamfights is almost always a terrible idea. Most of the time, the opposing team will steamroll your champion 1 vs 5 because you charged ahead. Only dive in if you are extremely tank-y and are sure you won’t die fast.