A loofah is not one to pick for exfoliation because people don't wash them properly and a lot of bacteria grows in them. Depending on your type of skin and sensitivity, try any type of granular exfoliant, and make sure it's like a sand grade rather than big chunks of things where you might scrub yourself raw. Your tan will slough off faster if you apply it to dry, dead skin. Also, you'll get a much more even application of the self-tanner when your skin is exfoliated. The self-tanners tend to cling to dead skin cells, and it will make certain areas darker if your skin isn't smooth.
Meticulous application is necessary.
The self-tanner makes you drier than normal, so you should definitely moisturize every day after you apply. The tan should last for a week, but longer if you top it off at home. There is no sun protection in self-tanner. When you apply a self-tanner in one session, even if it's more than one application, you'll be the same color. If you want to be darker, you'll have to do it another day.