League of Legends takes a lot of time to get good at. It has a pretty steep learning curve, but once you get over it the game becomes a ton easier. Most important aspects of the game is good decision making and being good at getting creep score.

Harass/Poke: Dealing damage without engaging a fight into anything.

Trading: Harassing/Poking an enemy champion and/or them hitting you back.

Gank: Picking off a player in a lane by surprising them (good ganks don't always result in a kill).

oom: Out of mana.

mia/ss: Missing in action/stay safe; Means their lane is not visible on the map, so be careful for getting ganked.

re: After someone leaves a lane and mia/ss is called, if they return this is usually said.

care: Play carefully.

b: Back off.

overextend: A rule of thumb when laning is not to be over extended to avoid enemy ganks. Many consider anything past the river to be over extended.

cc: Crowd control; stuns, silences, slows, etc.

Focus: Prioritize your damage on that target.

squishy: Fragile champion that will die if focused.

Fed: Having a huge lead in gold.

Pushing: Auto-attacking and/or using spells to kill minions quickly to move your creeps faster down your lane.

Last hit: Only dealing the final amount of damage to a minion to kill it and get the gold.

Force: Making something happen.

AP Carry: Champions that want to build mostly Ability Power, and most of their damage comes
from abilities.
EXAMPLES: Annie, Ahri, Cassiopeia, Anivia, Gragas, Fiddlesticks, etc.

AD Carry: Champions that want to build mostly Attack Damage, and most of their damage comes from their auto-attacks.
EXAMPLES: Kog'maw, Graves, Ashe, Caitlyn, Sivir, Vayne, Draven, Ezreal, etc.

Jungler: Champions that go into the forest areas of the map to farm the monsters and control map objectives, such as Red Buff, Blue Buff, Dragon, and Baron.
EXAMPLES: Nocturne, Lee Sin, Dr. Mundo, Amumu, Alistar, Udyr, Skarner, etc.

Bruiser: Champions that want to build some types of resistances and a little damage, whether it be AD or AP.
EXAMPLES: Irelia, Renekton, Udyr, Lee Sin, Diana, Rumble, etc.

Tank: Champions that want to build purely defensive.
EXAMPLES: Shen, Malphite, Cho'Gath, etc.

Standard AD Carry Build: Boots 3 Health Potion --> 2 Doran's Blade --> Zeal --> B.F. Sword --> Berserker's Greaves --> Infinity Edge --> Vampiric Scepter --> Phantom Dancer --> Guardian Angel --> Last Whisper


Standard AP Carry Build: Boots 3 Health Potion --> 2 Doran's Ring --> Sorcerer's Shoes --> Hextech Revolver --> Rabadon's Deathcap --> Rylai's Crystal Scepter --> Zhonya's Hourglass --> Void Staff --> Guardian Angel

Standard Bruiser Build: Boots 3 Health Potion OR Cloth Armor 5 Health Potion OR Doran's Blade --> Wriggle's Lantern --> 2 Doran's Blade --> Ninja Tabi OR Mercury's Treads --> The Brutalizer OR Phage --> The Brutalizer OR Phage --> Aegis of the Legion --> Frozen Mallet --> rest situational

Standard Support Build: Faerie Charm 1 Health Potion and sight ward (spend rest gold on them) --> philosopher's stone --> Boots --> Heart of Gold --> kage's lucky pick --> Mercury's Treads OR Ionian Boots of Lucidity--> Aegis of the Legion --> Shurelya's Battlesong --> situational

Standard Jungler Build: Cloth Armor 5 Health Potion --> Boots --> Wriggle's Lantern --> Mercury Treads or Ninja Tabi --> Heart of Gold --> Wit's End --> Giant's Belt --> Warden's Mail --> Frozen Mallet --> Randuin's Omen --> Guardian's Angel

Standard Tank Build: Cloth Armor 5 Health Potion --> Boots --> Heart of Gold --> Philosopher's Stone --> Mercury's Treads --> Glacial Shroud --> Aegis of the Legion --> Negatron Cloak --> Frozen Heart --> Randuin's Omen --> Force of Nature --> Shurelya's Battlesong

*Note: Champions such as Ryze and Skarner have completely different builds. Search a guide up such on www.solomid.net or www.mobafire.com to get a good idea on a general build (don't be scared to change the build a bit to fit your play-style, and also pick the highest rated guides).

*NOTE: Look up guides on solomid.net/guides or mobafire.com if your not sure what to build.

*NOTE: Most champions have specific "tags" that tell you how you should play them (Such as Mage, Assassin, Bruiser/Fighter, Tanks, and others.

ALWAYS BUY WARDS WHEN YOU GO BACK (ONE OR TWO)

Learn to kill creeps properly (100 creep score by 20 minutes is a decent score, unless your a support)

ALWAYS build situationally. If enemy has 4 physical damage sources, build an early chain vest (if its AP, get an early negatron cloak).
If your team needs more damage, get damage items (same with everything else).

If your losing your lane HARD, play super safely, don't try to trade with the enemy in lane, just get as much cs as you can safely get.

One kill is worth 12-13 creep score, so cs is more important than a kill.

A KILL IS NEVER WORTH A DEATH!!!!!!

Don't try to push your lane, just try to last hit.

Don't rely on other people unless you KNOW you can (played a lot with them before).

Never overextend without wards, or you WILL die.

Getting caught after the 25 minute mark can lead to an instant-lost for your team if the other team is playing well.

Good map awareness is key in this game (being able to see what is happening across the map by looking at your minimap often).

Pushing without wards is extremely dangerous, as you will probably just get ganked and die.

If you kill an enemy and no one on your team dies (and your strong enough), get your team to rally around
and take objectives (blue buff, red buff, dragon, baron, turrets) as this will basically make it 5v4 for you guys.


If it is your first time playing a champion, or you don't know how to build them, look around www.mobafire.com or www.solomid.net/guides
and look up your champion (don't follow it completely, build situationally).

Help your lanes if they need it.

Don't try to force things your team can't do.

Watch high-elo streamers and actually pay attention to what they do, it is very educational.

Standard Lane Composition: Bruiser Solo-Top, AP Carry Solo-Mid, Jungler, AD Carry and Support Duo-Bottom Lane (most optimal set-up).

http://solomid.net/guides.php?g=13150
http://www.mobafire.com/league-of-legends/build/the-general-guide-to-league-of-legends-195826
http://www.mobafire.com/league-of-legends/build/lol-terminology-151019
http://www.mobafire.com/league-of-legends/build/generic-guide-becoming-a-better-player-214191
http://www.mobafire.com/league-of-legends/build/warding-helper-more-than-your-eyes-can-see-54337
http://solomid.net/guides.php?g=6340
http://solomid.net/guides.php?g=12314