I am a co-organizer for two big events per year in Tampa - BarCamp Tampa Bay and IGNITE Tampa. I attend at least 10 conferences per year. There are 5 things that are required to make a conference great.
The Venue. The place that will be home to the conference is the foundation. Parking, rest rooms, layout, lighting, A/V, acoustics, size and more are all factors that affect how the audience perceives and experiences the event.
I guess under venue should be Internet Access. It is very important today for attendees to be able to text, tweet, facebook, snapchat, etc., especially about your event. To do that, they need quality Internet.
UX = User Experience is not a requirement so much as the focus of the organizer. Without the attendee, no conference. Speakers should be considering that as well.
Snacks. Under snacks, I will include food in general and beverages - coffee, water and cocktails. The WebRTC Conference in Atlanta and the CompTIA ChannelCon really did a good job on providing snacks, lunch, breakfast, beverages - all day. Charge extra if you must, but this is how you keep attendees in the venue. The Front End Design Conference is held in St. Petersburg FL every year. On the video, most people talked about the chocolate bacon and food. At BarCamp Tampa Bay, red velvet cake was a snack we provided every year - red velvet cupcakes or twinkies or something. It became a symbol of the event.
Speakers. I harp on this all the time, but the key to a conference is the content. The key to really content is NOT Power Point. Passion is the key. If you are not enthusiastic or energetic or passionate about the subject, why speak on it? Because you have to? How do you think that will reflect on your company or personal brand?
BarCamps are Un-Conferences, which means that the agenda is built that day from attendees that want to share with others or who just want to start a dialog. Passion is the common denominator here.
Networking time. Sharing and meeting others - Connecting - is why we go to conferences. The knowledge exchange in the hallways are gold. The connections we make are what make the memories. Make sure that you plan for plenty of opportunities for attendees to have Q&A with the speakers and to network.
Pictures, Videos, Social Media - all the ways that we can capture the moments, share them and spread the word. You want to make people not in attendance jealous enough that they attend next time.
It's a lot of elements (and not all are under the control of the organizers). As an organizer of an event, you want to WOW the audience - and the sponsors and even the speakers. Create buzz. Surprise them, sugar them, serve up great content, mix and mingle them, connect them and record it all. It's all about the UX.