For print publisher:
Top L corner, 1st page - name and address.
Top R corner - word count, underneath it, rights offered.
Half way down page 1 - Title, Caps underline, below, 2 spaces, by line, normal text.
Body of text - T Roman/ Courier, size 12, double spaced, start writing, only one par on page 1.
On subsequent pages, do not carry pars from one page to the next.
Margins, on all pages, R & L margins at least 1 inch, better, 1.25.
Write on one side only of A4, or in the US, standard letter size.
Ensure grammar and spelling is as correct as possible, If British publisher - English spelling, US publisher - US spelling.
Number every page in header, or footer - page number/total pages.
This is very rough, but will suffice for most publishers, you really need a layout guide, there are usually plenty of writing books in libraries with much better info than this bit.
For electronic publisher, read site guide lines, they are all different.