Follow up within a day or two via e-mail or voice mail, unless a time is already set to call or meet again.
Reference the meeting in the subject line, comment that you enjoyed the conversation, and recap whatever topic or idea was discussed in the initial encounter.
Ask for what you want—be it a follow-up meeting, a chance to make a proposal, the names of key contacts, or information per whatever you discussed in the initial conversation.
If a response comes, reply accordingly and keep things moving forward.
If you don’t receive a reply after two days, send another e-mail asking if the first one was received and if he or she needs anything else from you.
If there’s still no reply, call to assess the situation.