Blog as frequently as you can. For me it's at least three times a week, usually more. I do see the benefits of blogging frequently (via google analytics) but sometimes I don't have time to craft a complete post and instead will just post a description of one of my paintings from one of my venues (Etsy or ebay), along with a picture. This is still good for the seo however it is lazy approach and I don't recommend you over do it. The point is to get something out there rather than go for days and days without posting anything on your blog!
I'd like to share, a simple list I glance at each time I blog. It consists of these basic, but important reminders (adapted from http://www.dailyblogtips.com/):
1. Did I read the post after writing it? (You'd be amazed how many times, I'm in a hurry and forget to do this-lol.)
2. Is the post as complete as it could be?
3. Did I research any related keywords?
4. Did I think carefully about the title?
5. Did I link to one or more of my older posts?
6. Did I link to external resources when appropriate?
7. Did I check to make sure my links are working?
8. Did I include an interesting image?
9. Is this a good day for traffic?
10. Did I proofread and check my spelling?
Third and Most Important Tip:
Besides these things though, the most important thing is to have a certain degree of passion about that which you blog about and have those feelings shine through to the reader. It's a lot about your reader (not you necessarily) and what he hopes to find in your blog. Remember, they're reading because you inspire them somehow!