I'll offer advice as a rookie - since I'm new to the learning curve last year...
1st - watch these videos:
https://www.youtube.com/watch?v=N4AXfdAa3KYhttps://www.youtube.com/watch?v=ljyarOK1l30Biggest thing I learned -
let the call do the work! Go light on the pressure in a smooth stroke. Then you can vary the angle slightly, the pressure slightly, and where you play the call. You can run it on center of box and center of striker, center of box an edge of striker, end of box and middle of stiker, etc. etc.
Keep trying different variations until you get the sound you are looking for, and then try to repeat it.
I'm sure there are many more tips from the advanced callers, but this is what I figured out early on. Good luck, have fun!