This is pretty much to contribute to the 7 Essential Meta Q's.
I committed to this SE when it was in Area 51 solely because I am on a team competing in the FIRST Robotics competition, and because pretty much all SE sites have a high technical level, this site can really change a lot of FIRST teams. The only thing this website needs is more participants.
I think one way to promote this site is to get FIRST to promote it for us. The only problem is that FIRST is a K-12 competition primarily, but mentors also take part in FIRST teams. This might bring the technical level of the website down, but I still think that many high schoolers have enough knowledge to handle and contribute to this website properly, so would FIRST be a good place to get more users? I'll most likely tell my team to use this site when they have a building issue they aren't able to solve.
A second idea I have is to advocate to close some of the proposals on Area 51 that are related to robotics and bring them over here.
This post very nicely talks about this more: Would we be better off with a combined Robotics, Automation and Mechatronics proposal?
What are some other ways we can get people to come here?