If you want a range of sensitivities to constrain a max/min sens.
Play scout, start with a really fast sens and try to keep your crosshair over a moving or stationary bot target whilst running or jumping around, keep lowering your sens until you find the fastest sens where you can do this comfortably. You can have this as your upper bound on sens.
Play any class, scout/solly demo. Start with a really slow sens and keep your crosshair, or targets off the screen and try to flick quickly to said targets (or between targets). With a really slow sens this will be uncomfortable to do, keep raising your sens until you find the lowest sens that's comfortable for doing this. You can have this as your lower bound.
I'd recommend playing around your lower bound, but then experiment with your sens using these 2 exercises and try and find an optimum.
When you've chosen something, don't fuck around with it for a while, try and develop a muscle memory for that sens.
Don't think about how you're aiming or how your sens should be in actual games and just think about what you should be doing ingame. I've always found that I aim way better if I'm not concerned with whether I'm hitting shots and am concerned about what my team and I are doing with respect to positioning etc.