How to Fix Large Cracks in Drywall
Embed the tape in the compound immediately.
Lay the tape over the compound you just applied and use the knife to push the tape into the compound. If necessary, cut the tape in short lengths to follow the line of a really crooked crack.
If you bought fiberglass tape, you can skip the embedding coat of compound under the tape because it is self-sticking. Otherwise, you do everything the same way.
Warning: Fiberglass tape is thicker than paper tape, which makes it harder to repair invisibly.