Akin to the old saw about "only a fool has himself for a lawyer" is the rule that NOBODY should attempt to proof his/her own work.

The corollary rule that the proofer must know more about grammar, layout, spelling, punctuation, capitalization, etc, than the writer should be sufficient to encourage hiring a good proofer for anything critical.

BUT WHEN YOU DO attempt to proof your own -

A break of at least a day between composing and proofing is almost mandatory.

It also helps, as noted above, to print the work in a different font/spacing/layout than used for the original composition.

If you must "do it on screen" (assuming that's where you composed it) then at least open a copy and change ALL OF THE FONTS to a different typeface than what you used to compose.

When you can spot the difference between a normal "." and an italic "." on a printout, you may forgo getting a professional proofer - if working on something for formal publication - maybe.

The purpose and readership for your work will determine which references are best, but the Chicago Manual of Style and Websters Collegiate should be by your side and be used for common kinds of work. Note that it does take some skill/experience to learn when you need to look it up - for most of us.

John