I think of a phrase that is
- easy to remember (no weird words, not the name of a character)
- not used by a famous movie already
- unique enough so that a google search on the title will find my movie immediately
- easy to include in a spoken line in the piece
- evocative of the piece, so when someone has seen it, they can easily remember seeing it given the title
There are some exceptions, for example my intentionally-opaque short “INTERKOZMOSZ ALIEN AUTOPSY”