How to Lane

You have 6 priorities while laning. They should be emphasized in the following order:
1) Don't Die
2) Be in range of the creeps to gain experience
3) Last Hit enemy creeps to gain gold
4) Prevent the enemy champions from Last Hitting your creeps
5) Zone enemy champions to keep them from gaining experience
6) Destroy the enemy tower

Killing Enemy Champions fulfills all the conditions from 2 to 5. A Sacrifice Exchange should only occur if your team gets a kill + assist while the enemy only gets a kill, or if a high priority champion (carry or off tank) gets the kill on your team and a lower priority champion (tank or support) gets the kill on the enemy team. A sacrifice may also be warranted if the enemy team has the advantage.

There are four tactics that can be used in a lane during the Laning Phase:

1) Last Hit enemy creeps - this means hanging back in a defensive posture and only auto-attacking when you know you'll kill an enemy creep. This may also include Zoning an enemy champion with one or both of your champions, starving them and feeding you. Last Hitting is especially effective if the enemy is either extremely defensive (hugging their tower) as you can easily zone them away, extremely aggressive (trying to gank you all the time) as you will make them come to you and thus improve your situation against them, or when your team has lane control and the enemy champions are scared witless. If your enemy is just last-hitting then your best option is to Harass them. That will force them from the creep line and disrupt their whole tactic. Following this you can go for a gank if you have superiority and lots of room. Alternately, try and Push the Enemy Tower. In that way you are disrupting the enemy's last hitting capabilities and taking control of the lane.

2) Harass Enemy Champions - this is just like Last Hitting except that you are also attempting to weaken enemy champions with your attacks and abilities. While harassing, make sure to never commit to an attack and stay away from their side of the creep line for more than a second. Harassing should be used when the enemy is just Last Hitting or when they are trying to Push your tower. If the enemy is successfully harassing you then you should either try to Gank them if you're still in a position to do so or fall back into a defensive position allowing your tower to cover you and stop them from harassing.

3) Gank Enemy Champions - This means attacking with the intent to kill, often but not always with the aid of an allied champion from the jungle or another lane. This should only be performed when you are 80%+ certain that you can get a kill and get away or make a benefic exchange. If you fail then you could either lose one or both of your champions, or walk away with a limp after showing your hand. Either way it isn't good. Ganking is especially effective against an enemy who is attempting to Push your tower or against an enemy who his Harassing while you still have the advantage. If the enemy is aggressive and tries to gank you often, play more defensive and just Last Hit creeps, making them have to come to you, or fall back to a defensive position at your tower if they are much stronger.

4) Push the Enemy Tower - This means killing all the creeps as quickly as possible and moving towards the enemy tower with the intent to damage or destroy it. This tactic should be used extremely sparingly, especially before level 5. Before that time the amount of damage you can deal to a tower is minimal and insignificant. The only time you should attempt to push is if you have a very strong advantage, either because you are over levelled, they have been harassed down or the enemy champions are not present because they left the lane forcibly or by choice. In almost every other situation where you are able to push the lane it is far more beneficial to simply zone out the enemy champions and Last Hit them (#1). If the enemy team is trying to push your tower, let them! If they have the advantage then call in a gank from your Jungler, Mid or the other lane. If they don't have the advantage then either harass them or wait for them to come close and gank them yourselves!

5) Hug your Tower - Whenever you are getting overwhelmed or the enemy team is getting overly aggressive, fall back to your tower. When you are hugging try to either keep above half health or have a Heal spell ready so that you don't get killed by a sudden dive (from any direction). Hugging your tower can also be useful in feigning weakness. If your enemy thinks they have the advantage they will overextend themselves, allowing you to handily dispatch them under cover from your stone defender. If your enemy is hugging their tower it is usually best to fall back, zone them away from the creep line and just last-hit to your heart's content. The only exception is if you know you can dive and kill a champion or dive and deal significant damage to their tower.

6) Leave the Lane to heal/shop/gank - Whenever you are below half health go back to town! Even if your enemy is also low. If you're the first one out then there will still be a few seconds where they are wondering 'is he still there?' and when you return at full health they will be like, 'eep, he has full health!' allowing you to have more domination. When they realize that they too need to go back to heal you will know exactly when they are doing so and be able to carry on as you please. Pay attention to other lanes as well. If they are in trouble then try to go to their aid if you are able or offer to switch with them. If they are pinging like mad then go there IMMEDIATELY, even if they are on the other side of the map - your attention may be desperately required. If it turns out later that you couldn't help then go back to your lane - but you may have just turned the tides of the game with your quick reactions and team awareness!