I have a website, where I constantly add new information, so the site is changing. This is not everyday, but at least a couple of times per week. Newsletter, tips, etc, are put on the site. The content changes, but the subject matter does not. I want to keep the relevant in the search engine lists. How often should I update meta tags or does it matter since the subject matter does not change (same topics, new info)? Also, will changing meta tags too often "penalize" my site. I have never used a submission service because I was told they really don't work. Any thoughts on this. Any help is appreciated. Thank you.

"keywords" meta tags are not really important for search engine optimization. You can put them once and forget about them. And your "description" meta tag should be that sentence that will appear when your website appears in the search results.

Change your meta information as often as is appropriate. You won’t be penalized for changing your meta tags too often.