Grip with your thighs, not your calves.
Ride without stirrups first, then hop on bareback when your comfortable without stirrups.
Ride a horse you trust, one with nice gaits.
Instead of just sitting there, bouncing, post. It will make you grip with your thighs and I find it easier allbeit more exhausting.
For the canter, ride a horse that's responsive but not too much so, and one you trust. Loosen your reins a smidgeon and grab mane and get into a slightly forward seat and ask. As you relax, your position will reach where it should be. Also, first time cantering - do the straightaways. Corners can be tricky
And try it. I cantered bareback for the first time this past summer and I felt so accomplished with myself! Its such a great feeling <3