If you are promoting your blog or website, you should have accounts on all of the above. Login in often and post your website url with a little new info. Always post links to your newest blogs as soon as it is published. These sites are at the center of the social media universe...take advantage of them.
Now let's be a little more creative...
Post in discussion boards/forums
Search for similar topics
Suggest the link ("Thanks for the tip! This is another article that helped me out....")
Join discussion boards or forums that are pertinent to your website and blog info. Search these boards to find out what others are saying and "suggest" your blog or website as additional information for them.
Question/Answer boards (similar to discussion board concept)
Lots of people read Cragslist. Don't be afraid to post your site or blogs and just ask. Including a little humor may help.
Having a giveaway that randomly goes to someone that LIKES your page or retweets a post if very effective. If you have the ability, giving away an iPad is as good as gold. Services such as Wildfire and other contest apps can help with this.
QR Code Like buttons
People are quite curious about QR codes. Many people will "read" them just to see where they go. In this case, link to your site and your blog. It is even possible to generate a QR Code "LIKE" Button. When someone scans the code with their module phone, it automatically has them LIKE that link. Try it out below.
Finally, don't forget old fashioned groveling and hitting up friends and family. It's the same technique that gets you out of hot water with your significant other. Send them every blog post and just plain ask for the "like" or "retweet". When in doubt, offer to buy them coffee!
What other ideas do you have? Post in Comments below?