Harassment, being about half of lane control, is one of the most crucial acts of early game. Composed mostly of frequent non-lethal attacks, it's not very difficult to perform but can be very dangerous for less practiced players. In many situations, the early game advantage can hinge vastly on how well a team harasses and deals with harassment. Early game is all about gaining an experience and gold advantage as quickly as possible. One large part of that is Last-Hitting & Denying, but another equally important part is being able to keep the enemy heroes in your lane as far away from farming the creeps as possible through strong harassment.
Basic harassment is simple to get a grasp on. You just attack enemies once or twice whenever they are in range, just to drop their hit points a bit and scare them away. It is not necessary to kill the enemies in early game, quite to the contrary the experience they lose from the time they spend running to the fountain and back can far outweigh the amount they lose from the short re-spawn timer at low levels.
Avoiding Creep Aggro
If you guys could just stop attacking me, I'd really appreciate it.
The term "Creep Aggro" refers to creeps targeting their enemies, and switching targets appropriately. This is an important thing to know about when harassing because every time you attack an enemy hero within Aggro Range of their creeps, the creeps will switch targets and begin attacking you. The safest way to avoid being attacked by the creeps is to move into range of the enemy hero before issuing an attack command on them, then immediately moving away from the creeps. The creeps will move to attack you once you issue the attack command, but you should be able to move away before any of them are in range, and they will switch targets to your nearby creeps.
The problem with harassing that way is that it indirectly pushes the lane by stopping the enemy creeps from attacking for a second or two. Since that will eventually allow the enemies to farm near the safety of their tower, its generally bad practice. To avoid grabbing the creep’s aggro you should harass from the side of the lane furthest from the creeps and, if possible, from behind them. Being behind the enemy creeps allows you to push the heroes even further away from the creeps and deny them the experience they desperately need.
Creep Aggro Range
The Aggro Range of a melee creeps is 500. To give you a point of reference for this, that's normally just short of a ranged heroes attack range.
Orb Harassment
Don't worry. You never saw that.
The term "Orb Harassment" comes from the game Defense of the Ancients (DotA), and means attacking with a Hero's toggle-able attack ability. By manually attacking an enemy hero with the ability as if it were a spell you were casting, you can completely avoid the enemy creeps targeting you and harass in a much safer fashion. Currently the only heroes with these attack abilities are: Arachna (Webbed Shot), Vindicator (Master's Incantation), and Kraken (Splash).
Consumable Regeneration
You don't expect them to just sit there and let you push them around, do you?
Enemy heroes will attack and nuke you in response to your harassment. Because of this, heroes that will be harassing heavily will generally need a lot of regeneration. Most of the time this regeneration will come in the form of Runes of the Blight. These little tree eaters are a godsend to keep your health close to full at all times. Use them whenever you feel the need and don't hesitate to have a courier bring you more as the need arises. 90 gold is a small price to pay to keep those enemies from getting levels and gold for themselves. You can also bet on your enemies being clever enough to use regeneration items of their own. Keep an eye out though, because some consumable regeneration items, like Health Potions, are canceled when the hero under their effects takes damage. Whenever possible, interrupting these effects is a very effective form of harassment. Not only will you stop the enemy heroes from regenerating their health, or mana, but you will essentially "rob" them of the gold they spent on the item.
Mana Harassment
All your Mana belongs to Me!
Harassing an enemy's mana is a form of harassment exclusive to heroes like Vindicator and Witch Slayer who each have abilities that target an enemy’s mana. Every hero with abilities like this has a specific way of effectively harassing which will be detailed in their respective hero guides. It should be noted though that denying the enemy their mana often stops them from being able to effectively harass back, and gives much easier lane control than typical harassment will.
Prioritizing Tasks
Should you really be doing that right now?
While harassing is always good, not every hero should prioritize it. In general there are three tasks that need to be prioritized while laning: Harassment, Last Hitting, and Denying. A hero who is babysitting would probably prioritize Harassment over Denying, over Last Hitting, while the carry being babysat will prioritize Last Hitting over Denying, over Harassment. The point is that while you should always try to harass, in many situations you should try not to focus on it too much. Keeping enemy heroes from farming is nice, but if you or your lane partner don't get any farm either then what was the point?
