Here's a few things you might want to know if you already didn't:
1: Turret diving early game is an awful idea.
Basically what turret diving is when you get close to an enemy turret to try and finish off a retreating opponent. The result, at least in early game, usually results in a very quick death and is not the best way to start a match. Try to always play passive and wait patiently until your enemy makes a mistake.
2: Farm a lot.
Basically farming is the same thing as creeping in DotA, in which you kill the minions for cash. Remember though that you have to get the last hit to get the money, so time your attacks wisely, because farming is your main source of revenue early game. You can also try harassing, but that's not suggested. (Harassing is to continually kill someone while trading hits during laning phase, when you defend your towers/turrets.)
3: Cooperate in team fights.
Team fights is basically what goes about mid game and late game. Both teams come together to trade blows. You HAVE to stay with your team during this phase or else you WILL die if you get found, and team fights are hard to pull off when an ally is missing.
4: Terms to remember.
AP means Ability Power, which basically raises magic damage. AD means attack damage, which raises physical damage. Ganking is when three people are on a lane, while one is brushing (hiding in a bush) until the time is right to jump in and help, causing surprise to the enemy and, most of the time, killing one or both of the people in that lane. There are more, but those are some terms I didn't know when I started.
5: Don't give up.
Sometimes the LoL community can be really harsh on you if you make a mistake or anything. Don't get discouraged, all players start off that way. People will get better in time, you just need to practice a lot. It also helps to play with others of a higher skill than you, so then you can learn habits or tricks from them.
I hope this was a little helpful. There's a more to LoL than these five tips, but they were important tips I didn't know when I started LoL that I wish I knew. Good luck, and have fun! ^^