There are basically two jungling types; gankers and farmers. Gankers need to gank soon and gank early to maintain their dominance throughout the game. These are usually the people that can gank pre-6. Lee Sin, Udyr, etc. Others need to farm heavily and then gank, usually those that require 6 such as some of the AP jungles (Fiddle being the archetype). Knowing which one your facing will help you decide what you need to do. Within the ganker/farmer ones are people who are better at invading or resisting invasion. For instance Shyvanna lately has been shown to be a very effective at invasions/resisting due to her Burnout and Twin Bite but her ganks are considered sub par. Aside from observing their jungle in champ select it is very beneficial to have someone with Clairvoyance CV their base when the match begins. By knowing what the jungler has you can guess their routes. A Nocturne with a Vamp scepter is going for a very aggressive jungle and will probably be getting a heavy pull on blue and maybe even some help on red. So a first level invasion may not be a good idea unless you can see people on the other lanes. A jungler that starts with Cloth+5 pots is a conservative jungle and will probably be left to their own devices after blue pull, leaving you open to counter them after blue. Aside from the actual jungler there are some players that are very in tune with their junglers and may immediately move to help them in a counter. Other times and Im sure all us junglers have experienced this, despite a healthy amount of pings no one will move to help you at all and you can either run or fight. There are some jungles you should never go into, one primarily being Shaco. Shaco will always evade you and more often than not chasing him will result in running into a faceful of JiTBs. You dont see Singed jungle much but when you do chasing him around in his jungle is never good either, one of the primary LoL rules apply here; Never chase a Singed. Hope this helps a little.