If you're installing a new screen, skip the next two steps. Otherwise, follow the next two steps to clean and reuse your existing screen.

Use tweezers or the flat end of a spudger to peel up and remove large pieces of old adhesive from the screen.

Apply one or two drops of highly-concentrated isopropyl alcohol (over 90%) to any residual adhesive.

Only apply one or two drops at a time, and don't spill any on the screen panel itself to avoid damaging it.

Use a lint-free or microfiber cloth to wipe the perimeter of the screen clean.