Effective follow-up begins during the event itself. Note who asks which question, who shows interest in a follow-up and who makes specific remarks. That gives you material for a personal follow-up message.
Send a message to every attendee the day after. Not a generic thank-you email, but a short personal message that refers to something said or discussed. Also send the summary and the recording of the presentation. Within five working days, plan a concrete follow-up for people who showed interest: a conversation, a quote, a bespoke demo. A product presentation without a follow-up plan is an investment without return.