Submit only to agents or publishers who handle the kind of work you produce.

Don't staple your ms, present it in a folder or bound in any way
just put an elastic band around it.

Format your ms correctly:
12-point serif font
double-spaced on one side only
use good paper and a laser printer
leave reasonable margins

Don't write a huge essay about your book
in the covering letter.

You'll probably need to write a brief enquiry letter first, then you might be invited to send a synopsis and, maybe, three chapters or something. If you're lucky. If they say they like but it needs changing, change it.

Don't send the whole thing unsolicited.

Don't phone. Anybody. Ever.