Lots of email, phone calls, and online approval.
If they offer no input at the start, I'll ask for some. But typically, no client input indicates that they have hired you in part because they trust your instincts. Most of my clients come to me because of something else they've heard that I worked on, so my assumption is that they like most aspects of that particular job. That gives me a good frame of reference before work begins.
The best situation is when the client is comfortable with multiple online approval passes. It certainly is no problem for me to upload WAV files, wait for customer approval, tweak as needed, and repeat until things are right.
This can be done via the mail, too, of course... but only when there is no deadline to speak of (rarely the case).
