I have never submitted a crossword to a paper, so these disconnected ideas may not be worth the memory they're occupying. However�
Make sure the crosswords you're sending fit the style and difficulty of the publication you're sending to. Solve a reasonable number to check.
The Times has about 90 stock grids and it's no use submitting a crossword on a grid you made up yourself.
According to "The Crossword Obsession" by Coral Amende, American puzzle editors will send you a style sheet, if you ask. I don't know about British ones.