Coalition events are better than solo events. More people, more skills, more experience, more energy.
Get relevant permits. Know your rights - look them up.
Establish a single organizing point of contact.
Establish a single press point of contact.
Prepare press releases, including the one for after the event. Read a document or book about writing press releases if you don't know how.
Establish the twitter hashtags for this event. If it's a small event, it's better to use an existing, relevant hashtag for the topic, rather than to invent one for yourself. For example, #schooloftheamericas is better than #oct2SOA, because people are searching for the first one. Search for the tags first, pick from the good ones.
Call your people two months ahead of the event. Find out who can signal boost for you. Make sure big events aren't happening that day.
Identify key bloggers and key press to contact in person.
Prepare flyers: print flyer 8.5x11 in color and b&w, test printing in b&w because colors like red become black, and blue can become light gray. 1/4 page for flyer drops. 500x500 memes for facebook, larger image for others. Test the online graphics for visibility and readability. Make a Vine video if you think it'll help. Polished YouTube "ads" can work well - get someone good to shoot and edit it. It'll take a week or more to make a video ad.
Create an event in Google Calendar, make public. You can link to it and the reader can get the ICS file to add it to their personal calendar.
Create an event in Facebook. Invite all your friends or followers.
Post the event to this site, http://la.indymedia.org/. Consider using meetup.com to find existing groups that should be interested.
Email blast the event a couple weeks before event, then again 3-4 days ahead. Post to the main email lists in LA - dopexresistance, laamn, changelinks, actionla (? is it still going) - and any specialized lists in the community. Finding lists is hard - try yahoogroups, google groups, and riseup.net's lists.
Tweet the event regularly. Tweet during the day, not late at night. During this time, build the twitter list - follow others, personal message them, and do follow fridays.
During event, "live tweet". One person can do this. Don't tweet everything. A few photos is enough. Spend time reading other's tweets and retweeting if they comment or post about the topic. Post photo galleries later to facebook, twitter, and this site.
Have press contact available for press, obviously.
After event, post prepared post-event message (edited post-event of course) to social media.
Share media coverage to social media.
Longer term, find out who are active in social media with hundreds or thousands of followers or readers. Make sure they have the right followers.