Use the products.
First the adhesive remover to get rid of all traces of adhesive from the previous appliance. Don't skip this, as it also cleans up skin oils, etc.
Second, the "prep" wipes. These get the skin ready to receive the adhesive.
You can find combo cleaner+prep wipes. I never liked these as much as the separate ones. YMMV.
Third, there's the dust. This is optional, but a godsend if there's any skin irritation.
Finally, apply the appliance. Push the sucker down for a while (like a full minute).
Of course, the really tricky bit is getting all this accomplished while keeping the area clean & dry. I used applesauce, marshmallows, and the paper towel "volcano" technique - let me know if you want more details on this.
Note that different companies make different adhesives with different effectiveness depending on specific skin types. Keep trying different ones until you find one you're satisfied with. The companies should be delighted to send you samples to win your business. I wound up with enough samples to get me through nearly a month. Don't let your providers talk you into committing to one supplier before you've found the one you like. For me, Coloplast was great; Convatec was terrible. Again, YMMV.
And of course, one adhesive ring is only supposed to get you through about four or five days, give or take two. Stick time is reduced by intensive sweating and exercise - though you should be able to get a good sweat on without actually dropping your bag.
Good luck.