The more you play the more you will see what your options are. Take into account who the opposing jungler is and what his likely route is, and what your team's lane matchups are. Sometimes you will need to hang by a specific lane to help ensure they make it to mid game. Sometimes you will need to ward key spots that the laners are not already doing.
Always always always communicate where you are headed, and hopefully they communicate with you as well if the river is warded, or tri bush, or wherever. When going for a gank consider everyone's positions. If your teammates are pinned against your tower try going from the river. If they are pushed a little ahead then try approaching from your lane and hiding in the side bush. Again this is based on whether or not certain spots are warded. If you approach, and see them immediately run back, there is a ward and you should either try a different angle or go elsewhere.
If you score some early kills, feel free to buy strong items that will help you kill easier. If the game is balanced or not in your favor, buy more defensive items. You want to be able to sustain yourself in some way. That is why most junglers have some sort of lifesteal/regen.
You can't be everywhere at once, no matter how any stupid teammates will lead you to believe. They need to be able to take care of themselves, press advantages, and defend when outmatched.
Overall just keep practicing and use whatever champ fits your playstyle.