Keep track of important monsters
The timers are:
Golem/Wolf packs -1:00
Wraiths - 0:50
Lizard Red Buff - 5:00
Golem Blue Buff - 5:00
Dragon - 6:00
Baron - 7:00
Deny enemies experience by leaving units alive in the jungle
"A monster camp only respawns after its fully wiped out. If you are killing monsters in the enemies jungle, you can leave a single unit alive in a camp to prevent it from respawning, denying them gold and experience points."
Time your Smite right
"Smite always deals exactly how much damage is indicated in the tooltip (true damage). If you check your smite damage and keep track of your targets health (by left-clicking it and looking at its status panel), you can time the smite just right to prevent enemies from stealing the kill."
Get to the Windmill faster in Dominion
"If you want to start a Dominion game going towards Windmill (top-center point), follow the fog of war bridge to the haste pad to get there quickly and covertly."
Morgana's Dark Binding can find hidden foes
"You can tell if you hit a target as Morgana with Dark Binding if youre not at full health, and see your health jump up a bit (because of her built-in spell vamp)."
Ward killing 101
"Using abilities that generate multiple attacks or auto-attack resets (Shyvanas Q, Renekton W) can be really useful for killing wards before they become stealthed."
Use Rumble's flamethrower without moving
"Using Rumbles Q and then pressing H holds him in place, so he can still flame things, without necessarily having to get close to scary things like towers or champs."
Use Rumble's flamethrower to move faster
"If you use Rumbles flamethrower while running back to lane, you can get into the danger zone, where he moves 30% faster, thus getting you back into lane faster."
Lock on to invisible units
"Abilities such as Tides of Blood, Soul Shackles and Death Lotus can "lock on" and target invisible units, firing their projectiles and damage as normal."
Vlad's Tides of Blood is a heat-seaking missile
"Vlads Tides of Blood hits whatever is in range, whether or not you can see it- can be valuable when trying to hit a target you know is in a bush and trying to Recall."