Relatively new to the game myself, but one thing I notice is people constantly attacking their laning opponent, ignoring CS and objectives. It's as if they think that constantly attacking is the only way to play this game.
Also, as a jungler, gank at level 3. period. Just do it. Sure, there are exceptions, but do it. Oh, and ganking doesn't mean walking into lane in FRONT of the enemy (unless you're lane ganking through the bushes). go around behind the enemy champ. It's insane how many times I see my jungler (yes, only silver :)) literally walk into lane, take a few CS and seem surprised when I'm not thankful for the "gank".
Learn 1-2 champs for each role. I'd recommend sticking with those 5 - 10 champs for 50 games each (bans/picks aside)
as a laner, you're jungler can't help you as much if you're constantly pushed up to the enemy tower. Also, when your jungler comes, or pings 'on the way' don't immediately attack the enemy champ thinking he's already there! I have so many ganks where I'm 5 seconds out and my mid will go ham on the enemy mid laner, scaring them back.
If you killed the adc or support bot, and the other champ stays, don't be afraid to dive them at their tower if your jungler is still around.
some matchups you just won't win 90 percent of the time. Learn which ones those are and learn how to survive till laning is over. example: teemo vs nasus or gp vs panth. one of the hardest counters I went up against :(