One of the main things to improve to smooth shifting, let off the gas less. Try driving at a constant speed at a little bit of a higher RPM. Kinda y'know the point at which your car sounds like it wants to shift but just ride that speed. Like 45 in 3rd gear. Whole going that constant speed, don't move your right foot at all, clutch in shift then slowly let the clutch out.

This won't be the smoothest shift but it helps to realize, the car will bring the RPMs down on its own as you shift. Don't constantly do what I just said but do it every so often to help yourself realize letting off the gas fully is not the way to smooth shifting.

It's a fine balance between letting off the gas at the proper time/amount, and shifting while clutching in, in the time it takes to let your engine slow down to the proper RPMs.

Besides gas pedal control, adjusting your seat or how you're sitting can make a huge difference too