People aren't very good at reading between the lines and doubt could mean they don't buy a ticket for your event. To combat this, put up a website well in advance and make it very easy to find out:
- event location
- event date
- prices of tickets and how to get one
- schedule or structure, basically what to expect and why people should be there
- how to contact you
These are the absolute minimum. My recommendation is that you will also want to include (as early as this information can possibly be available) any extra items such as the dates and times of any social events (so people can include those in their travel plans), travel advice and/or directions, and for bonus points local knowledge such as where to stay, local facilities, etc. One year the PHP London conference did a full set of directions complete with photos - I can't find those now but I loved the idea and did something similar for PHPNW09.
Without this kind of information, people are much less likely to do the work to find it all out themselves, or may not feel confident enough to come along. I've also been bitten by events where the info was sketchy and the event turned out to be just as sketchy! Where the information is easily available, transport links are listed, and contact numbers given, the experience has been much smoother and more pleasant all round - this is especially relevant if you have speakers or attendees travelling internationally who may feel a bit lost when they are trying to make their way to the venue.
Make sure you also pick a hashtag for people to use when they are blogging or tagging tweets or photos, that way your attendees can start to make links with one another (and on a more negative note, you'll see when people are complaining and you can respond!). Already you are building the community that will make your event a success ... and if you've done all of the above then rest assured that you are absolutely on the right lines!
If you have any more tips, share them in the comments, I'm sure there are things I either missed or don't even know I should be doing!