I don't tweet much, but I use the hell outta twitter. It's just another resource to find news on a variety of topics. I have multiple twitter accounts, do this primarily to separate my online / personal identity.
Agree with
@TerryP, look and see who people are following to get an idea of who you want to follow is a good way to start out. Once you see people who are tweeting stuff you care about, just follow them and it will get added to your timeline.
I love TweetDeck, it's UI is much better on the computer vs a mobile device. The downside to using them is sometimes there are changes in twitter functionality that take them a while to implement. Example, when Twitter went from 140 character limit to 280, it took TweetDeck weeks (if I remember correctly) to adopt this in their code. You can have columns that search for #hashtags, show your lists (where you group people by topics, show other peoples tweets, etc. I don't use the twitter app/ui very often.
If you don't like the tweets someone has, you can now mute them, previously you're only option was the unfollow or block. So if you get tired of reading someones nonsense, mute or unfollow them. It's your timeline, put what you want in there...