One small, universal tip that will help a jungler's ganks tremendously

Save your slows/roots/disables/whatever your kit has for when their laner attempts to escape, not when you're initially ganking the lane.

Let's say you're playing Rengar, and you're ganking top lane. Because the Scuttler is often a handy tool to charge your Ferocity stacks ahead of time right underneath the lane, your Bola Strike is ready to go to root them when you get there.

Yeah, don't do that. Never, ever use that (or any skills you don't have to, excluding his Q and W, because they can't miss) when you're just within range, even if you have a clear shot, primarily for these reasons:

1. It's a lot easier to miss.
2. If they can, they'll probably try to Flash out, reducing its effectiveness, or possibly causing you to miss even if point-blank.
3. They'll be running past their minion wave, so you can minimize or avoid entirely minion damage during the gank.
4. No minions can get in the way of you or your ally's skillshots when they start to run.
5. They'll be out of cooldowns to use against you to stop both you and your ally.

It's such a simple thing to keep in mind, but it can easily make the difference between a successful or failed gank. Let them react first to your showing up. Let them Flash if they're inclined to use it. Then use your disables appropriately, and burst the hell out of them with your ally.

This also includes Kayle junglers, because I love you and want you to keep playing Kayle jungle. Don't blow your critical Q slow or your W speed boost until they begin to run.

salutes Fellow junglers, you are the true unsung heroes of any secured lane, and the precise source of toxicity on their team. Keep putting their weak link on tilt, and you'll keep walking away the victor.