Every time you die, look at what killed you. What happened?
A mistake a lot of players make is to play way too aggressively, in which case there are four things that can kill you:
1. The enemy champion. If the enemy champ is stronger than you, they can and will turn and fight. If you die early, you are throwing your lane - if you keep trying to fight, they will find killing you easier and easier. This is why earlygame bush 2v2s are a bad idea unless you are definitely stronger than the enemy, and that's hard to judge as a new summoner.
2. Enemy minions. Minions actually really hurt, especially very early game (<lvl 5). If you autoattack the enemy champion, their minions will turn and start attacking you - step into a bush to shed minion aggro. This doesn't work if you attacked out of a bush, so try to step out of the bush, hit them, then step back in. Also, if you hit them with a skill the minions won't aggro.
3. Enemy towers. Don't take free damage, from enemies in general but especially from towers.
4. Enemy teammates. If you're pushed very far, you will have enemies come down the river to kill you. Try and only last-hit to kill minions, so you don't push. Also, buying wards so you can see the river will make it much harder for enemies to take you by surprise.