At least what I do:
Detailed, hard core, up to the picosecond literature search. Nothing will sink a proposal faster than someone else having tested and published on your hypothesis. Even the old farts who think not only do they know the entire field, but that they invented it, do this (at least the good ones).
This is not always easy. I did a theoretical thesis so I would not have too much literature to read. But done it must be.