A step-by-step guide to Twitter
Step one:
1. Sign for the service on twitter.com
2. Install Tweetdeck, a platform that makes sorting your Twitter categories easy.
3. Follow people: But not those who haven’t filled out their Twitter profile or who have never tweeted or who look like spammers or porn. (Check the Web site link in the bio.)
4. Check followers of people who follow you: it’s a good way to wrack up followers at first.
5. It’s fine to just follow friends if all you want to do with Twitter is converse with people you already know. But you can follow people you don’t know especially if they are twittering on a subject in which you’re interested
Step two: What do you tweet about?
1. Tweet your blog posts: But don’t just say “New blog post.” Explain it: “Just blogged about Fifth Summit of the Americas."
2. Tweet about other things: Tweet other people’s blog posts or stories that you find interesting. (A good way to do that is to say “Reading …” and give a summary of the post, and, of course, a link.)
3. Tweet general observations: Yes, tweet what you’re having for lunch — just not every day.
4. Retweet other people’s post that you admire: Retweeting pays off. If you do it; others may retweet your posts. Plus you’re providing more value to your followers.
Step three:
1. Use hashtags: A hastag is a keyword that you type in your tweet along with a # sign. It makes any tweet with that word aggregate on one page.
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Judette Coward Puglisi (MSc, Dip IR, BA), Managing Director. Find out more 
The fact is people will follow your corporate Twitter feed because they are interested in what your organiastion has to say.
This makes perfect sense if you are an information based organisation or consumer oriented. In both cases, you may be seeking as wide a audience as possible to get your messages out, and the people who follow you want to hear what you have to say.
Typically I check out the bios and tweets of those who've made a request. This is my screening process
I like Twitter for the conversational tone and not for the broadcast elements, there is a fine line between both.
Another way to get people to follow you on Twitter is to make full use of hashtags (#). This will aggregate all the responses of all the folks interested in your subject area, it's like forming a like-minded community.
Here's another great way to increase the number of followers. Go searching for new people to follow on Twitter. It is fine to look for people who have a connection to your community/product/service. You'll find that as you increase the number of people your corporate Twitter account follows, the number of people who follow your organisation, will rise , as well. If your organisation has a blog, even better. You'll get more hits.
Oh, and to your question about separating your personal and professional account, take a look at this debate that was started by my colleague, I'll leave you to make your own judgement. Check this link: http://tinyurl.com/dyg7r7
Hope this helps