Make important actions easily undo-able. Gmail does this right. In Twitter, if you miss the 'Accept' button (it happens when you're a klutz like me) you hit the 'Block' button. That makes no sense, why would Block be so close to Accept? And then you can't just undo that. No, no you can't.
Yes, this also means I finally reactivated my Twitter account. No, it doesn't mean I'll be using it.