just do what is comfortable,, but for the love of god make sure that you can use all of the trumpets features. In England, even only at county youth level we were told that not using your slides is like not using certain valves. while i think this may be an exaggeration, i know that the conductor (a trumpet player) would not accept anyone into KYWO unless they used valve slides appropriately. Personally I have my little finger under the 3rd slide, my middle finger through the ring, my ring finger out of the ring, on top of the 3rd slide and on the bell side of the ring. my index finger resides on the 3rd valve casing. I think this is unusual but it works.