I've done over 400 free speaking engagements for corporations, in exchange for the opportunity to promote my services (personal training). Now, I'd like to start doing paid speaking gigs. I've done 4 paid speaking engagements in the past, but they kind of just fell into my lap. I'd like to be more deliberate about it.
Read Allan Weiss - he has sales processes for consultants - one of which is getting speaking engagements.
Specialize - specialize - specialize. Be really clear on what people get out of your speaking that is special to you (they can't get it anywhere else). Join associations and give a free 20-minute teaser and then at the end that you go into more detail at your speaking sessions (which you can rent a location and charge admission or solicit companies to have you come in).