I use twittbot.net (not .com, .net) because I have no programming skills, am unoriginal, and have a vague grasp of what character is what in katakana. It looks really sketchy, but it's not bad.

• First off, log into your bot's Twitter.
• Then, try logging in with that big ol' light blue button on Twittbot.
• The captcha is weird. Don't worry about it.
• It's gonna ask you for permission to screw with the Twitter you're logged in on, a la privatter or twitlonger. You're gonna want to allow it.
• Once you've done that, on Twittbot you can go to "tweet" (the first option after logging in), type in your tweets in the space provided, hit "add", and there you go!

If you're ever uncomfortable, you can just revoke permission on your bot's Twitter. (I did that for a little bit for joker_ebooks_, even. You're okay.)