Different Ways to Gank
Casual Entrapment. A lot of ganks begin as a game of entrapment. You, as a lone hero, scout an area and find an enemy hero, which would most probably try and chase you down; it's human nature to feel superior against another who bids a hasty retreat with your presence. This works to your advantage.
You can set the trap prior to baiting the hero, or make your allies aware of the enemy following your tail. They can come to your assistance to help you dispose of the threat. If he chases you closer to your territory, it will be harder for him to have any support from his teammates, especially if he follows you blindly.
At some point during the game, this kind of gank become too obvious for the experienced player, and will realize that he is going too deep into enemy territory, and back off.
Scouting Jungle. There are some popular “jungling” heroes, which do not play on a lane, but rather kill the creeps in the forest. These heroes should be ganked if possible, since good junglers can make a good amount of money without disturbance from enemy heroes.
Usually, heroes who farm the jungle early game push their hitpoints as low as possible. Catching them at a bad time would spell an early death for such a player. Keep an eye on the lanes – if there’s one less hero, he’s probably killing creeps in the jungle. Use the command –ma (to see the enemy heroes’ level) and –afk (to make sure that the player is indeed playing and not idle). If the “missing” enemy hero is not afk and is gaining levels, then scouring the woods by yourself or with a teammate every so often is a good idea to disturb and kill a jungling hero.
Good Old Ambush. The traditional, most straight-up way to gank a hero is simply considered a heat of the moment opportunity, where one takes advantage of a given situation. Many times, heroes will venture too far out of their safe zones when they are unopposed by an enemy for some time. Moving through the forest to ambush the hero is standard for DotA games.
How to Avoid Ganks
The concept of avoiding ganks is easier said than done.
To ultimately avoid being a victim of ganks, the most important thing to keep in mind is map awareness. Checking the minimap every so often makes you more alert regarding enemy whereabouts. Early game, heroes tend to stay on one lane most of the time.
If one enemy hero leaves his lane, there are a couple of things that he could have done: He can either have gone back to the fountain to heal and buy some items, check runes, or ultimately, orchestrate a gank.
As part of a team, it’s somewhat your duty to call missing heroes. This means you should tell your allies that your lane’s enemy heroes are missing in action. You can do this by simply typing “missing (your lane)” or any variable of that such as “mis bottom” or “mia top”. This would greatly help your allies be more aware of their surroundings as well.
Another way to avoid ganks is investing in the purchase of Observer Wards. These items give you a line of sight on areas where heroes might attempt a gank (such as forest entry and exitways) so you can move away when you see incoming enemy heroes.
Effective Heroes for Ganking
Some heroes are best at lane control, some heroes are best at tanking; logically some heroes are best at ganks -- here comes a list of the more appropriated heroes for ganks, divided in several categories.
This might be the most useful category for ganks -- all of these heroes have very powerful abilities that allow them to kill an isolated hero quickly.
Lion (Demon Witch)
Probably the most deadly nuker in early game thanks to his powerful ultimate -- Finger of Death. Catching a hero unaware and using the stun and hex combo, plus the ultimate usually spells death for most heroes at low levels. Coupled with a teammate, it's deadly!
This hero is very similar to Lion. Indeed, just as Lion, Lina owns a deadly ultimate which deals 450 damage at level 1. Also, Lina has a stunning spell (Light Strike Array) and an area-of-effect spell (Dragon Slave). In a team, Lina and Lion combined make a lethal early-game combo.
Tinker is the best nuker of DotA mainly due to his two powers -- Heat Seeking Missle and Laser, which deals more than 600 damage combined. Boush's ultimate is also very useful, it refreshes all of his powers and item cooldowns.
Lich is a perfect hero to hunt and gang in woods since his ultimate is made to be casted when there are several units. Make sure to use your ultimate when there is at least TWO units nearby (including your target hero) since the nova needs to bounce between units. Casting it while there are too many units makes it less potent, as it might not hit your target hero more than once.
Akasha (Queen of Pain)
Here is one of the most dangerous heroes of DotA, at anytime of the game. Because of her blink ability, she can enter and leave the fight easily and cast her spells. She can surprise an enemy with Blink and catch them unaware, initiating the gank. She also has very powerful spells that allow her to deal a lot of damage to her enemies.
These are all the heroes which are very good launching surprise attacks due to their skills which can make them invisible or can help them scouting.
Anub'arak (Nerubian Assassin)
Anub'arak is THE hero made to gank, give him a Dagon and he can get rid of anything. Thanks to his ultimate which allows him to become invisible and deal up to 525 damage at higher levels. He can also stun and mana burn his opponents. Attacking while invisible (ultimate) deals damage, combined with the mana burn and stun damage usually spells death of several low hp early game heroes.
The main point of playing Rexxar is using his pets. Indeed, he has a power which allows him to call two animals -- a Quill Beast, which can slow his targets, and a Hawk, which become invisible at level 4 and allows you to follow every move of one hero. Plus, his ultimate is kind of very powerful because of its cooldown and its stunning ability.
Rikimaru (Stealth Assassin)
This little guy owns an ultimate which makes him invisible permanently when he is not attacking. One of his spells -- Smoke Screen -- inhibits the casting of spells and cancels channeled spells in its area of effect. The biggest advantage of playing Rikimaru is that you can change lane or go to the woods very easily, since it's really hard for the enemies to know if you are gone or not.
Gondar (Bounty Hunter)This hero is made to hunt. His ultimate -- Track -- allows him to move faster, to see the prey he casted his spell on and gives him a gold bonus if he manages to kill it. He also has a powerful nuke -- Shuriken Toss – which deals direct damage to the enemy. He can also become invisible and deal extra damage thanks to his critical strike ability.
Luna (Moon Rider)
Luna is one of those heroes you cannot fight in a single duel. His ultimate casts until 16 Lucent Beams on every enemy units in the area and so deals a lot of damage. If you are all alone against Luna and he uses his ultimate, you will take all the Beams and probably die. Equipping Luna with Lothar's Edge is always smart -- you just need to find an isolated hero, make sure he is not circled by too many allied units and cast your ultimate for an instant kill!
Chen is the best "foresting" hero due to his ability to control creeps and give them extra life. You can control until 3 creeps and use their powers which are stuns, slows or net. He can also slow his enemies and deal them random damage. He has also the power of healing all his allied heroes wherever they are in the map.
Balanar (Night Stalker)
Balanar has two sides. By day, he is not very useful -- he does not move and attack very fast and his powers do not have special characteristics. However, by night, he becomes close to immortal. All of his powers are buffed and gain extra effects, like slow or silence, and he moves and attack very fast. That's why Balanar is made to be discreet by day, and gank everyone by night.