How should you separate meta tag keywords

When it comes to laying out your meta-keywords, you have two options

<search,engine,submission> (commas between words, with no spaces)
<search engine submission> (spaces only)

Separate your keywords with commas, but if you want to form phrases out of the individual keywords then leave a space between the words and bracket the new phrase with commas

e.g.<search engine submission,add url,ranking,position>

Some words of warning

Be careful if you use meta-tags as a place to put in misspellings of keywords that you spelt correctly on your page, as some search engines (including AltaVista) penalise web pages that contain keywords in the meta-tags that cannot be found on the page itself
Make sure any meta tag used is not broken up over several lines, as this is not correct, it should all be on one line. This applies to both meta description and meta keywords in your page
Note that it is possible to accidentally repeat a meta-keyword multiple times when you use a word in different phrases: e.g., a meta-keyword tag containing, "search engine promotion, search engine ranking, search engine placement", would have repeated the words "search engine" three times even though they occur in different phrases. Some repetition is apparently acceptable (possibly even up to three times); excessive repetition is regarded as "spam"

However no S/E will penalise you for the correct use of meta-tags so make sure you use them, they make up an essential element of your search engine optimisation and web site promotion strategy

Case sensitivity

Consider beginning each word in your keywords list with an initial capital letter. For example <Optimisation,Ranking,Add url>. There is evidence that this will help since some (not all) search engines treat search criteria differently if it is an initial cap

If people where to do a search for "add url", most search engines would return results containing "add url" and "Add url", however if someone searched on "Add url", some search engines would return only listings that contained "Add url"

Using the right keywords in your site's meta tags won't shoot you to the top of the S/E's, but if done correctly can help in achieving a better ranking.

Summary

Meta description and meta keywords should be page specific. Meta description is what users see in search engine result page, so make sure it's informative and inviting
Only put words in your meta keyword tag if they are already in your page text
Don't repeat a keyword in your Meta Tags more than 3 times
Review the code of your competition and see what keywords they are using