Re: Multi-tasking includes proof-reading?
The best way to avoid, no reduce those errors, are to give the thing to someone with no or little experience or knowledge of the topic - they tend to read what is there.
There are various tricks proofreaders employ which can help. One way to catch spelling errors, for example, is to read the text backwards, from last word to first. That makes it more difficult to read them as what you expect rather than what's actually on the page.
Similarly, some people mark up hardcopy of the text in various ways as they read, as a way to help catch fine (word omissions, homonyms, etc) and gross (structure, logic) errors.
Others find that reading aloud helps.