The general rule on Twitter is that if someone follows you, follow them back.
I suggest doing a search on Twitter for your target market - that's what I did and just followed them all lol.
Don't forget to use hashtags in your tweets - your tweets are easy to find then!
Another thing I suggest is to get a 'daily newspaper' at http://www.paper.li
. It's automatically tweeted every day at a certain time. You can choose to include tweets from your feed - so often people you're following will be included in it. It's a great chance to get retweeted!