Immediately follow up to get feedback from the event coordinator. This is the perfect time to solidify your relationship and ensure a repeat performance.
Ask them for a testimonial letter, even if you have to write it for them. I also ask if they have other topics they are looking for and if I don’t speak on the topic, I’ll introduce them to someone who does. I like to be remembered for being a resource, which will encourage them to call me for additional resources in the future.
I will also ask for a referral to other speaking engagements. It seems that everyone has contacts in their industry and once they have said they enjoy my presentations they will almost always know exactly the right type of people to refer me to for additional speaking engagements.