For those not in the know, an older, now defunct 3d graphics.SE never made it out of private beta.
What can we do to make sure Blender.SE has the best chance of at least making it out of private beta?
There are several variables involved but the major one is publicity. Even in our commitment phase which took nearly a year, I myself had no idea of it until I randomly stumbled across it. What we need is publicity. IIRC every Blender release totals around at least 200k downloads which means that there are lots of people out there, people who want to learn.
My main suggestion is to share the site wherever and whenever you can, tweet a well written question or answer you found useful and or share a new tip or trick you learnt via your social and personal pages. Invite or tell a friend.
This site is a refreshing take on Q&A and Blender in general. It also helps us to stretch ourselves from dusty IRC channels and lengthy confusing forum threads. Lets make this into a great community!
Voting is important.
It feeds one of the stats on the Area 51 site (Avid users) which is used to determine how well this site is doing and whether to keep it running.
If a question receives a lot of votes and/or comments, it can end up in the "Supercolider" which is the "Hot questions" section of the main dropdown at the top of each page. This brings a lot of users to that question from other parts of StackExchange. I don't know if this happens during the public beta (and it certainly won't during the private beta) but when it does, even obscure questions can end up with hundreds of votes and dozens of answers.
Voting also encourages new users to contribute more by "rewarding" them.
Voting is also important in the long-term. Once the site is well established, the votes on the answers is how people who find a question through search engines can tell which answer is the best.
Another important difference with the 3D graphics SE is that the Blender SE is more specific. It is about one program instead of a whole area. It's hard to see as a user of the 3D graphics SE which subjects are in the scope of the site and which aren't.
Therefor i think that a specific Blender SE has a lot more potential and change of success than the 3D graphics SE.