Hi Slicepong
Good question. Ideally you want to have a relaxed grip but this does vary between player to player. Take Timo for example his grip is tighter than Ma Longs. And Waldners grip is more relaxed than both of them 🙂
I would say try and practice with relaxed grip with around 5% tension. With your thumb and index finger use a slight bit of pressure and your other 3 fingers wrap around the bat loosely.
In terms of the placement of your index finger use what you find most comfortable. Try not to have your index finger to high but a little bit is okay. If its too high it can be hard to exchange from backhand to forehand.
