Before the event

'Static' (or one-off) activities

Update your signature (Outlook plus Hubspot) to include a Call To Action (CTA) for your next event. You can use Hubspot to create your basic signature, and edit in a live html editor
Put a diary marker in for the day after the event to update your signature!
Pinned tweet - advertise the event via an attractive, engaging tweet pinned to the top of your account
Banner advert/'Call to Action' (CTA). Put a diary marker in for the day after the event to remove!
Organise media partners and incentivise them to support your event with free tickets
Advertise the event with meta-sites such as Fatsoma
Identify your top social media supporters via Hubspot, and consider how to engage them with promoting the event. Very high profile social media performers should get personal attention from senior staff members
Engage a skilled colleague or professional photographer to take photos during the day

'Ongoing' activities

Email potential attendees via appropriate segments of your email list, and have monthly mailshots leading up to the event. If your event management platform is tied to your email platform, send different ones to registered attendees vs unregistered
Promote via the LinkedIn showcase page. If relevant, a daily update on new attendee figures, new attendee companies. Every week highlight sponsors and exhibitors. Same on Twitter, Instagram and G+

During the event