Two sided market places are appealing because - at scale - they are hard to disrupt. Rarely are they easy to build (i.e. there's no secret or piece of advice that's going to help too much, other than embrace the mindset this will be hard work for a while: you can't just launch a web product and wait for magic to occur - you need to work hard at business development).
Google, Facebook & LinkedIn are audience models that grew so large that parts of them are effectively two-sided market places (well, I'm being generous towards Facebook, but Google's ads and LinkedIn's jobs are sometimes what I'm looking for). This can be an easier approach to scale, though it requires content that appeals to your audience and investment to pay for the content prior to the revenue strategy.
eBay, Uber and AirBnB are true 2-sided marketplace examples. eBay focused on power sellers - people who could list a lot of items quickly. I'm not familiar enough with Uber, but they've clearly focused geographically. Same, I believe, with AirBnB.
I agree with everyone who tells you to start by focusing on a niche to build both sides at small scale yet high saturation, but I'll add this dimension for you to think about: pick the focus such that it becomes possible to get to 50% of that tiny niche in a purely manual fashion. In other words, restrict your business down until a couple people with phones, email addresses, spreadsheets and a willingness to hustle can get you real traction. If you restricted yourself to just NYC, for example, could you meet all the players in person in a year? Or should you restrict it to a specific type of job - could you find everyone online who has that specific job title?
Choose the focus to try to make your life easier - the task is hard enough to begin with. If you can get things rolling, you can look to add another niche to expand to. However, if you are thinking you'll focus on one side of the market and then deal with the other later, you have an audience business model like Facebook, not a 2-sided market like Uber. Make sure you have real, sticky content like Facebook in that case. For Uber, the other side of the marketplace *is* the content... without it, "focusing" on just one side isn't going to help much.