Always max Q first on Rengo, then usually you want to max E second. The most typical rengar build is this (its what i do on him almost every time). Rangers trailblazer with warrior enchantment (to help with sustain)...2nd buy CDR boots..3rd buy Tiamat...4th buy Brutalizer and then finish it into Yommus Ghostblade (after finishing this youll have 40% cdr if you have 5% from runes)...then build a Last Whisper...then finish your Ravenous Hydra...last item depends what your going up against (either a defensive item or a 6th offensive item if your carrying the game). You should be looking to use his ultimate every time it comes off cooldown immediately (but dont force a bad gank or assassination, if its not there then just wait for the right moment). Ideally you only want to gank with his ultimate (which is part of the reason for wanting the early 40% cdr). But its not an absolute necessity, you can gank without it. But if you dont have the ability to jump onto the enemy (you need his ult or a bush for this) it makes it more difficult to do. Rengar is all about the element of surprise and deleting someone before they have the chance to react. And as for the dragon, Rengar is really really squishy so i wouldnt suggest trying to solo drag. He doesnt have the amount of sustain or damage per second you would need to do it efficiently. Oh and youll have to learn when to use his empowered Q or empowered E first when you jump on someone. The only reason you would want to use his E sometimes is because when you have 5 ferocity stacks, his E will snare the enemy for 2 seconds. So it basically acts as a stun. Using this in ganks helps a lot! But youll just have to get the feel for him and learn when to use empowered Q or E. Hope this helps a bit!