Help on follow-up email!! Thank you!!!

Hi guys,

I have a question about follow-up email. How to follow-up after a phone conversation besides asking for referrals? I'm trying to come up with some specific questions to ask but I really can't think of any at this point. It has been a month since I spoke with some of them so I think I have to follow up to stay on their radar. Is it a good idea to ask questions like "What can I do now to better prepare me for a specific group?" What kind of questions are good to continue the conversation?

Thank you guys!