Here is how I do it. Standing while leaning against a wall.
1. Find a flat wall and stand with your back towards the wall.
2. Unfold the diaper and make sure that the leakage barriers are loosened from the diaper and standing up. The leakage barriers on Tena Slip diapers are often stuck to the diaper.
3. Hold the diaper in the rear wings with both hands behind your back and against your butt.
3. Position the diaper so that the wings go around your hip and over your thighs. The diaper should often be placed lower on your back than you think.
4. When you think you have it position correctly, lean back on the wall so that the wall hold the diaper in place.
5. Now with two free hands, pull the diaper up between your legs and stretch it out around your body.
6. The diaper should be around up to your belly button. The front wings should go above your legs. A common mistake is to place the front too low so that the front wings go over the legs.
7. If you feel like you can't get the diaper up high enough, just lean forward a little bit and gently tug and readjust the front.
8. Repeat step 3 to 7 until it feels good.
9. When it feels good, take the right or the left front wing and stretch it up and to the side. Make sure that you don't have any wrinkles and that the wing is flat on your hip. And also make sure that the middle of the diaper is still centered on your stomach.
10. While holding the wing with the opposite hand to the wing (left hand hold right wing and right hand hold left wing) take your other hand and attach the bottom tape in an upward angle towards your belly button. The tape should be placed in the middle or lower middle of the wing (so you still have space for the upper tape).
Be sure to not have your other hand (that is still holding the front wing) under the back wing while attaching the tape.
And be sure not to pull it too tight or you risk ripping the tape or the diaper ends up not centered.
Rather pull on the front wing than the tape.
11. When the first bottom tape is attached. Go to the other side and do the same thing.
12. When you have attached the two bottom tapes, re-flatten, restrectch and recenter the front wing and then attach the next tape. I usually do every other side.
13. Do the same thing on the other side.
14. And you're done. It will not be perfect the first times but I assure you that with practice comes perfection