5. Don't overextend. Try to stick near a (your) tower. In this game, (your) towers are your friends. Use them.
6. Try to keep track of where all your foes are at all times. If all your enemies are MIA, its probably not a good idea to dick around in the middle of your lane without putting down some wards first.
These are all the places you can/should ward. The most important places (during the laning phase) are at the ends of the river that lead into your lane. These are where ganks will come from; it's nice to know ahead of time when you should get the hell out. 75 gold WILL SAVE YOUR LIFE. Later on, keep dragon and baron warded. Now, the job of warding generally falls to the support/jungler. However, if they're not doing it, do try to keep at least 1 ward on you so that you can do it yourself.
This takes a while to learn, don't worry.
7. Learn to teamfight. Set up an order of who to kill before fights actually start. Generally you want to look for vulnerable squishy heroes who deal tons of damage, and kill them first. Make sure your entire team is focusfiring all they have on one person before moving to the next. Enemy tanks are always last.
Let the tanks initiate. They have the CC and can take those hard hits.
If you're a squishy, don't get initiated on. Because if you get caught, the natural response is to run away. And when you run away, that's time spent not doing any damage and being completely worthless. Of course, you will eventually get caught out of position. If you KNOW you won't make it out, do as much damage as you possibly can before you get killed.
8. Learn team composition/lane setup. A good (generic) setup is:
Annie, Ryze, Brand. These heroes generally take mid, because:
a) Mages have better early games than autoattackers
b) solo laning gives them a level advantage; this level advantage means they get their ults faster. this means they can gank.
c) being in mid puts them in the best position to gank top and bottom lane
Ashe, Caitlyn, Graves, Trynd, etc. These guys usually take bottom lane with the support. Why?
a) Generally speaking, they are poor early game
b) If they were to solo lane, there is a good probability they will get shut down, leaving them useless in the mid to late game.
c) Being with a support enables them to farm in relative safty
Soraka, Sona, Taric. They duo bot with the AD carry.
a) They buy the wards so that the carry can farm safely and not have to spend money on such things.
b) They are basically a battery pack. So obviously the best place to put them is with a hero whose early game is poor/not much sustain.
Amumu, Rammus, Shen. Generally speaking, they jungle.
a) Tanks generally have poor laning presence. They don't have too much harass, and are 'all or nothing' type of heroes. This is not good in the early game when creeps do tons of damage.
b) Sitting in the jungle lets them farm in relative safety.
c) Because these heroes have a lot of CC, they are some of the best gankers. Being in the jungle adds unpredictability to their ganking patterns.
Irelia, Yorick, Lee Sin. These folks usually solo top.
a) They have a ton of sustain. This makes it so that when the jungler is ready to gank, they can actually participate in a relatively healthy state.
b) Their job is to just be really tough to kill, and do a good amount of damage to boot.
c) Some of these folks can also jungle; it depends on the player/teamcomp.
If you have more than one of each type, your team becomes much easier to counter via items.
9. Farm is super important. 1 Creep = 30 gold. That means 10 Creeps = 300 Gold. That's right, sitting in lane for two creep waves (and getting most of them) is equivalent to killing an enemy hero. So why gank if you could get just as much gold farming? The point of ganking isn't just to give gold/exp to yourself, its to deny your enemies the opportunity to farm, AS WELL as push enemy turrets. Just wanted to clarify that. There's no point in ganking if you don't push down a turret.
10. Learn to counter enemies via items. If you're getting stomped on, it doesn't matter if you're a carry, GET SOME DEFENSIVE ITEMS. In games vs people who know what they're doing, glass cannon builds are just retarded. Tank items, on the other hand, are relatively cheap compared to their damage counterparts, and help you survive those pesky ganks.
If you're getting your ass kicked by mages, get a Banshee's Veil.
If you're getting your ass kicked by autoattackers, get a Thornmail/Zhonyas.
You can also counter defensive items. Are you an Ashe fighting a Rammus with 90000 armor? Grab a Last Whisper. Are you a Brand fighting a Galio with 200980808098098908 magic resist? Get a Void Staff. Learning how to build is KEY to success.
11. The best heroes in the game (at least when I stopped playing) are (in no particular order):
Low Level Play: These are the heroes that are god tier when nobody else knows what the hell they're doing. They stomp, and they stomp hard. HOWEVER, against a person who knows how to CC/CS, they are very manageable.
Master Yi, Singed, Garen, Mordekaiser, Tryndamere, Leblanc, Katarina
High Level Play: These heroes are very solid picks, even against people who know what they're doing.
Akali, Nidalee, Graves, Amumu, Rammus, Galio, Ryze, Irelia, Lee Sin, Rumble
12. Don't be an asshole.
13. Play with friends who you can chat with on Skype.
For me its always been the opposite. I hate carries, and love playing tanks
Tanks are probably the most important character type in the game, and can be a ton of fun to play. They are the ones who decide when shit happens, and on what terms. Unfortunately, beginners don't really know when to initate or when to back off. And when you do play a good tank, at beginner levels nobody ELSE knows how to SUPPORT the tank, or how to GO IN WHEN THE TANK GOES IN. Then when you die, they'll just yell at you for 'feeding'.