No one tapes my diaper better than I do.
It's because I have diapered me more than anyone else. My wife does a pretty good job, and I never turn down her offers, but in the back of my mind I know I do a better job.
My free advice:
Stand with your back near a wall.
Unfold the diaper and put a crease down the middle of the diaper the long way.
Place the back of the diaper between you and the wall.
Adjust the height so the waist is where it feels right.
Reach down and pull the front of the diaper up.
One hand in back and one hand in front, move the diaper up and down until it is snuggly into the region around your thighs.
Pull one side of the diaper back snuggly, and tape the bottom tape rather snuggly.
Repeat the process for the bottom tape on the other side.
Go back to the other side, pull the top snuggly back and tape the top tape aimed slightly down.
Repeat on the other side.
I don't adjust after that, and with the top tapes aimed slightly down, the diaper will not sag even if it is soaked.
Good luck!