My tips:
-Laying down is better than standing or pressed against the wall. It lets you get the position exactly right.
-Make sure you get the back and front about even with each other. If you're going to be laying on your belly for that diaper, then you can cheap to the front some, but other than that you need to have them about even or the fit will be off and you will be prone to leaks.
-Pull the front up and snug against your lower tummy. Once it is centered, use your opposite hand to smooth out one side of the front over your hip. Then use the hand on that side to pull the bottom most tape up and stick it onto the front. Slide out the hand you were using to position the side at the same time - you dont want to tape over your positioning hand, or when you pull it out you will have a looser fit than you were trying for.
-As noted above, angle the bottom tape up. I like to make sure it is taped on my pelvis bone, not down on the thigh. Then repeat with the bottom tab on the other side before moving on to the middle and top tapes. If you do all three on one side at once, you will likely pull the front off center to that side, which will make the fit uneven, uncomfortable, and prone to leaking. Some people go bottom, bottom, top, top, middle, middle. I personally go right bottom, left bottom, right middle, right top, left middle, left top. Getting the top two tapes in exactly the right spot is less important than the bottom tape.
-You want your legs positioned approximately how they will be when you are wearing the diaper. I.e. if you;re going to be sitting, then bend your knees so your thighs are angled away from your abdomen similar to when you are sitting.
-As mentioned above, don;t let anything get on the tapes or their landing spot. Baby powder or oil on a tape will completely ruin it. If you are using oil, lotion, rash cream, etc., you might consider applying all that to your diaper area and then washing your hands, then putting your diaper on. Powder can just be shaken directly into the diaper, it doesn't need to be spread over your diaper area with your hand.