To start this isn't about invading and killing the enemy jungler.

While related that is beyond the scope of what I want to discuss, which is what do I look for to know I have a good chance of getting in and getting out of the enemy jungle?

So first thing, if you don't know where the enemy jungler is the answer is no*. Stay out except for shallow excursions to steal their raptor camp and quickly drop shallow wards. Even when you do this watch the enemy midlaner's position. If they start moving toward you turn around.

The main time I go into the enemy jungle is when they are ganking on the opposite side of the map.

Why?

Because they aren't going to surprise me in their jungle.
Because I can't get cross map in time to help my laner.
Because the jungle camps on the opposite side of the map are probably up if they are farming efficiently (e.g. Clear 3 camps on one side of the map and gank).

What do I ask myself?
  • Do I have any wards to drop?
  • Do I have a good escape mechanism if I do get collapsed on by their laners?
  • Is there a ripe gank opportunity that would be better to pull off than counterjungling in terms of getting my team ahead?
  • Can the enemy jungle counter jungle me on the opposite side of the map if their gank is successful?
  • Have a I recently taken the scuttle crab on that side of the map so if I have a hasty retreat, I can use the speed shrine to increase my odds of escaping?

What do I do while I am in the enemy jungle?
  • Place wards
  • Smite the wolf camp if Blue side
  • Smite the raptor camp if Red side
  • Look to steal as many camps as you can get away with without getting caught.
  • Watch the mini-map at all times to see if their laner disappear which likely means they are coming for you.
  • Consider laying an ambush for the enemy jungler
  • Consider that you may be behind their ward line which can give you avenues for ganking from an unexpected direction.
  • Look for tower crash dives (diving the enemy laner at their turret when your minion wave crashes into their turret) from behind walls if you have a way to get over walls.

What if I encounter a ward, especially one that just gets placed?

If you can, kill the ward then leave. Simple as that. If you encounter a ward or the wolf spirit then you've been spotted. There is no point in spending more time in that area than necessary, go do something else, preferably moving in such a way that they enemy team loses track of you (one way of thinking about this is don't do the obvious. Don't just leave their jungle and go whack on scuttle crab unless you have their jungle/river well warded because it can be pretty obvious to figure out where you are and possibly where you will be just from showing on the map briefly...be a little cagey about it).

*exception to this rule would be if your Mid and Top or Mid and Bot laners have their lanes pushed to the enemy turrets and you don't have anything to farm in your jungle. Then it can be reasonably safe to counter jungle because your laners are close enough to help you if you get into trouble and their laners will usually be busy trying to CS under turret which in a lot of instances will keep them busy unless they just drop everything to collapse on you.