Fundamentally, The Twit Cleaner exists to help you become a better Twitter citizen - and to surround yourself with the best possible people.
Of course, there is value to following news feeds (all links) or celebrities (no follow back) etc but here are some tips on how you can be a better member of the Twitter community.
Retweet
Retweeting (whether old style "RT @name message" or the new style) is a great way to do several things. First, it shares valuable material with your followers. Second, it's a way of saying thank you, & passing kudos to the person you're retweeting.
Obviously the more you retweet, the more people are likely to retweet you, spreading your message far beyond simply those currently following you. This, of course, is also likely to get you more followers.
Now, you don't want to retweet too much (or only retweet), because also important is:
Personal Content
Just posting links all the time - while informative, doesn't give people a feel for the kind of person you are. People don't want to connect with a company (or a bot), they want to interact with other people. That's what's so great about Twitter, it enables human connection in a way that blogs & old media really don't.
Now, this doesn't mean telling everyone what you had for lunch, necessarily (yawn!), but remember - you're a human first, and a content spreader or news provider second.
Engage! Connect! Communicate!
@reply to people who say interesting things. Reply to those that talk to you. Firstly, it's polite. Secondly, it's a great way to make friends, discover exciting new opportunities, and, frankly, one of the greatest things about Twitter.
Now obviously people with zillions of followers won't necessarily be able to reply to every single comment made to them (much like restaurants, the rules for celebrities are slightly different than for us normal folk), but at least make an effort.
If you never talk to anyone, how are you any different from an RSS feed? Youtube, TV or a newspaper? You're not. Besides, there are so many wonderful people out there - it's fun! Start chatting!
Variety is important
Posting the same link over & over is tedious - and people switch off from that very quickly. If you're losing followers, or all your followers are dead accounts? That'll explain why.
People aren't stupid. They're not on Twitter coz they want the same thing repetitively rammed down their throats. If they wanted that, they'd be watching adverts on TV.
Same goes for posting the exact same tweet over and over. That's just ridiculous. Now of course, if you have a product launch, or you want to attract people in different timezones, you may need to repeat yourself a bit - but mix it up. It's not hard to rephrase things, try different wording & so on. If nothing else it keeps you more interesting - but also, it's basic human psychology that people respond to different stimuli (verbal, aural, visual, mental imagery, etc). So, it's actually smart to vary your message - you're more likely to appeal to a greater audience by doing so.
Don't go crazy
While Twitter can be a very exciting place to be, churning out thousands of updates a day is just going to flood people's tweetstreams.
If you're following 40k people, it can be very easy to forget, but 90% of active users follow fewer than 2000 people. If you include all the half-arsed dead accounts out there, it's probably closer to 98%. If you are posting 50 times a day, you're going to flood everyone else they care about off their front page.
I've analysed a ton of accounts, and it's actually pretty hard to set off the alarms in this regard - & of course, if all you're doing is chatting to people, that's totally fine - since conversations with them only go to them (& anyone else following them). If every tweet you do is public though? Maybe tone it down a little, for the sake of everyone else out there. Quality, not quantity, remember?
Getting feedback
If you want to know how you're doing on all these points? When you're logged into The Twit Cleaner now, on the front page, there's a link "How do I look to The Twit Cleaner." That'll tell you exactly how you're doing. It'll also give you tips on how to improve your game & get even better in the future.
The basics
Other than that - try to follow people back (if they appeal). Don't @ tons of people in one tweet (except RT's & follow friday, of course) - either talk to one person, or just DM them.
Oh, & one last point - don't sell crap on Twitter. Seriously, if people want white teeth, they'll google it, or, & here's a crazy thought, talk to a dentist.