Congratulations on the launch of the community!
I suspect the first question many people will have is about the purpose of the community. What role does is serve for your customers? What do you want them to do within it? What makes it unique etc? Is this a customer support community or do you want it to be something more than that?
How many members do you have and how many are you expecting? What is the total audience size? What kind of retention rates do you have from the customers you have now?
What is the current flow of your customers? What are their habits? To whom and to what do they pay attention to? That's probably going to uncover the biggest wins.
There are plenty of snazzy tactics you can try to get attention, but typically it's best to find the one thing that really matters and do it well. The biggest impact is usually having something so remarkably amazing in the community that it draws people however they hear about it.
Leaderboards don't tend to have much of an impact until the community is already quite successful.