I’ve got this dremel-type handpiece I use for work that’s a godsend for prepping. Turn down the RPMs, pop in a bur that isn’t too abrasive, slowly and CONSERVATIVELY prep the nailbeds. This seems to create longer lasting results compared to just roughing them up with a file.
Use alcohol to dry and clean the nailbeds (I tend to re-dry as I apply just to clean up any oil or sweat that may transfer from my hands as I work).
Layer as follows: A dot of glue, one of those jelly sticky tabs (hold w/ even pressure for ~20sec), another dot of glue, false nail (press and hold these as well). It’s not made for nails but I’ve been using Loctite Professional recently, seems to do better than any nail glue I can find locally.
They usually stay on solid for a full week or close to it, at which point I’m getting sick of my set anyway and want to either switch out or live unencumbered by long nails for a while. If you buy durable sets, and are careful when removing, they can be reused after scraping off any residual adhesive.
Using the tab-and-glue method not only makes them easier to remove if necessary, but also reduces pop-offs since the tab acts as a shock absorber, whereas using only glue keeps them in place but is also brittle and will crack the second you jam your finger on something. The one caveat is that it’s not great for sets that are translucent at the cuticle, as the tab stays visible unless you have some serious skills with the glue.
Loath though I am to recommend Shein for anything, there are some actual good sets on there among the flimsy trash, and at a buck or two per set, it’s by far the cheapest way I’ve found to have nice looking nails whenever I please.