Welcome. What Fishy said about it being difficult to enter early is true. Experienced volunteers sometimes have early entry (but usually not first-timers) or hardworking types who work on a theme camp Build prior to the playa, and are given early entry by a camp leader.
You can sign up for local mailing lists here, maybe meet some local camps near you whose build you can work on:http://regionals.burningman.com/na_index.html
You can sign up to volunteer via this link, but it can be overwhelming the first year; best to pick something you would like even if there is no advantage beyond satisfaction, and start with just 1 or 2 shifts and maybe add another at the event if you're happy. http://www.burningman.com/participate/volunteer.html
No matter when you arrive, there will no doubt be someone in need of your skills whether you are solo or in a group, and repairs are an amazing gift out there. (Some of friends of mine do this during hours of their choosing, and never lack for business). You can have "office hours" and hang out a sign, or keep it informal & introduce yourself to your neighbors as a handy guy in times of need.