Pushing is assisting friendly minions in stacking and moving up a lane, with the primary goal of doing damage to or destroying an enemy tower. Additionally, pushing is helpful by allowing you time to take your attention off of clearing enemy minions and being able to grab a side harvester or buff, or even assist a teammate in a gank.
Heroes who are effective lane pushers have two primary advantages over other heroes: wave clear and sustain. Wave clear is important because it allows the pusher to remain in control of their lane. Whatever the reason may be, it is very likely at some point that your lane will be counter pushed by the enemy and you will be facing a couple stacks of enemy minions attacking your tower. Heroes that possess good wave clear abilities do not need to worry about this eventuality as much because they can very easily equalize the waves and even begin a counter push of their own. Sustain is equally important because heroes who possess good wave clear abilities are mana hungry, especially in the early game. Being able to survive in lane for a longer period of time allows you to defend and push your lane more effectively. Both of these characteristics make an effective pusher, but also make them effective at early game harassment, especially in the solo lane.
For a list of effective pushers, see this page.
Pushing is an incredibly easy technique which has even more incredibly powerful impacts on the course of a game. To understand how to effectively push, we need to understand that there are three different kinds of minions (excluding super minions) and how they work. Each wave of minions will contain three melee minions who will need to be in immediate contact with the hero, tower or other minions to deal damage. Each wave will also contain one ranged minion. The ranged minion can attack at a distance of 1000u. The final type of minion is a siege minion. These minions spawn with a varied rate that you can read about here. Because siege and ranged minions are the primary damage dealers of the minions, they should always be your first targets when attacking minions, regardless of whether or not you are a lane pusher.
Lane pushing is not as simple as clearing a wave of enemy minions, however. To give your minions a chance at surviving the onslaught of the next enemy minion wave as well as the tower defenses, you need to get your minions to stack. Stacking is when you get multiple waves of minions to attack in one group. To get minions to stack, you must obey these two rules:
- Kill ranged and siege minions as soon as possible
- Do not attack melee minions (except for last hits).
(Additionally, a third rule of keeping as many of your minions alive until the next wave arrives could be applied, but this is rather difficult to accomplish in the early game against an effective enemy pusher. This is a strategy called a slow push.)
This strategy works because by prioritizing ranged and siege minions first, you're eliminating the minions that would otherwise not be taking damage (melee minions always clash with each other first) and assuming you clear the siege and ranged minions before any of your minions die, you are giving yourself an advantage in numbers. The advantage in numbers is the most critical aspect of pushing and rule #2 helps to further that. Not attacking melee minions (except for last hits) keeps your minions out of enemy tower range for longer. This allows them time to reinforce their numbers with the next wave of approaching minions before being wiped out by a tower. By the time your reinforcements arrive, so has the next wave of enemy minions at which point you start back over at rule #1 and continue. Buying your minions time to stack is what makes pushing work. One wave of minions is not much of a threat to a tower. Three waves of minions on the other hand, can do significant damage to a tower if no enemy hero is there to stop it.