The invitation process largely determines the turnout for your client event. A good approach consists of several steps.
Start with a save-the-date, at least 8 weeks before the event. Keep it short and intriguing — enough to reserve the date, not so much that you give everything away.
Send the official invitation 4 to 6 weeks in advance. Make clear what the value is for the invitee. Describe what happens and why it is relevant to them.
Have account managers or board members follow up personally. A phone call or personal message increases turnout considerably compared with an email alone.
Send a reminder 1-2 weeks before the event with practical information: venue, parking, dress code and programme. And call no-shows again a few days before the event.
Consider creating a sense of exclusivity. A limited number of places or a personal tone in the invitation makes the event more appealing.