Not Updated For Current Season
Always get health potions.
Farm: Get minion kills (CS) - grants gold so you can build better faster and don't continuous hit a minion - turn off auto attack - only go for the killing blow.
Push back the enemy champion unless you have low health, if that happens, get back to under the tower as soon as possible.
When attacking an enemy tower, it is important to just attack the tower by using Q, then use your basic attack to continuous hit it. If you use your Q and your E has either 4 upgrades or is maxed, use it on the enemy minions so they won't wipe out your minion support. If there are two of your minions left, get the hell out of there. Later in the game, tower targeting you won't that big of a deal because of warmog, but keep an eye on your health. If there is an enemy champion under their tower, don't attack it. Just use Q on the tower and go to the grass. If you hit the enemy champion, the tower starts targeting you.
For me, I like to get Q fist rather than E. WIth Q, you can deal a good portion of damage, essentially scaring the enemy champion so you can farm in peace. It also increases your movement speed for about 5 seconds, so that to your advantage, even if you end up not hitting something.
E is important to max first as it awesome for farming.
Get W third as it is important for you to get to +30 armor by the end of the game
Get R as soon as possible as it deals a larger amounts lower the health of the enemy champion is
It is important to have a teammate if there are two enemy champions in your lane against you. It is good if they are long range as they can hit the enemy from a distance, but the con is that they steal cs more easily.
Use your teammates as bait - hide in the grass and wait for the enemy to get ahead of you so you head back and hit them with the ol' Q-E (and maybe R after that if their health gets low enough) combo.
Heal and Dash. Those are my favorite spells since I have been in many an occasion where I have R almost ready, like 3 seconds, and then I die. Heal is great in how it gives you some health to survive a little bit longer. Dash is used when you have low health and there is a fast champion chasing after to you. Another great opportunity to use it is when there are more than 3 enemy champions in your lane, trying to kill you.