Leeching and Cobra Strike

Leeching allows you to take a percentage of the physical damage you cause and gives you life and/or mana so anything that will help boost your physical damage output will help make greater use of your leeching percentage. It should be noted though that as it is based on physical damage physical immune critters do not let you leech from them and there are also some creatures that do not let you leech life and/or mana (various types of skeletons don't). Finally in 1.10 a new property was added to monsters called drain, what this does is dictates how effective leeching is on that creature. 100% drain means it's at full effectiveness while 50% drain means you'll only get half of that (you have 20% life leech and cause 100 physical damage to a 50% drain creature so only get 10 life back).

Cobra Strike provides a great means for melee builds to keep their life and mana levels up as it can let you leech over 100% of the physical damage you cause in even the very early skill levels. It is still bound by the regular rules of leeching though. Cobra Strike does not add to your damage though, it just helps you refill your life and mana levels. Considering how useful it is every melee build should have a point in this skill but really you only need the one point as +skill items and ways to help you do more physical damage (like Tiger Strike charges) will do the rest for you.

You can leech using leeching items with any attack that causes physical damage (except Blade Sentinel) including kicks and ranged attacks but Cobra Strike and the other charge up skills do not work with ranged attacks, only melee attacks.