Marketing on Twitter..

My only advice would be to not do it repeatedly... one post occasionally rather than (as I have seen some do) one every few minutes. And maybe use your twitter indirectly rather than directly such as writing a blog and posting the link to twitter (some blogs do this automatically).

I stop following people whose twitter feed is all self-promotion. Engage in interesting conversations. Post interesting links. Be an interesting person to follow, and people might check out your book. (And yes, posting occasional news about your books or writing is fine, but don't let that be the majority of your tweets).

What I have observed is that when people are obviously marketing on twitter, it is less effective than when they are an interesting person to follow who occasionally posts about a book or news or contests.

~suki

Hash tags only work if you're jumping in on a trend. It's a great way to track conversations revolving around a particular topic, search for conversations related to your field, or hosting chats around hashtags to aggregate tweets relating to the conversation topic. Personally, I don't think they are super effective since there is no real standard for using them.