There are some excellent guides on warding like this excellent guide.

Some helpful tips on placing wards without coming close are given hereand here.

However with 4 simple wards its possible to predict every jungle gank. the only way to gank without being spotted by wards is going though the lane of a friendly champion or by jumping over a wall.

For the exact placement of the wards see the guide posted above

Jupie ward placement

red is for the purple team and blue for the blue team