Facebook CEO Mark Zuckerberg inevitably gets asked a lot of questions about how to succeed as a start-up.

Yet Facebook is long past its start-up days, and the company's latest public town hall meeting at Mobile World Congress 2015 in Barcelona gave Zuckerberg a chance to impart some of his knowledge on staffing issues and avoiding growing pains.

Here are his top five staffing tips:

1. Employ people you'd work for...
Zuckerberg said he developed a "simple rule" that helps him make hiring decisions. "I will only hire someone to work directly for me if I would work for that person," he said.

"What it means is that in an alternate universe if things were different and I didn't start the company I would be happy to work for that person, or if Facebook just disappeared and I had to go find something else to do that I would be happy to work for that person. It's a pretty good test."

He described chief operating officer Sheryl Sandberg as one example.

2. ...And who 'get' your culture
Zuckerberg spent much time at Mobile World Congress outlining his vision for Facebook. "We have a very strong opinion on the change that we want to create in the world," he said. So it follows that Facebook "is not a company for everyone in the world". He was interested in people that agreed with the company's vision, but added: "If you don't, then maybe find a different [company to work for]."

3. Don't bow to pressure
You may face the pressure of growing pains but Zuckerberg advises not to give in when hiring new people. "There's always this pressure where there's always more work than you have people to do it," he said. "That leads you to want to get people in to help you out and do that work, even if they're not the very best people.

"You could compromise a little bit on quality today and still get a bunch of better work done in the next six months because there's so much work. But over the long term you're really only going to be better off if you get someone really good."

4. Once you hire them, trust them
"As a general rule of management, if you get someone who's really good as part of your team then they need the ability to fully exercise all their creativity and all their capacity, else they're not going to be having the biggest impact they can have on the world and they're going to want to go do something else," Zuckerberg said.

5. Try to stay small
Facebook serves over a billion users worldwide, yet it has approximately 10,000 staff. This is no accident, and correlates with Zuckerberg's mindset when he set up the company, where he did most of the early coding himself, and brought on people only when they were absolutely needed.

"I generally at each step along the way have tried to do as much as I can myself or as much as our team can by itself without necessarily trying to take on more people," he said.

"I find that that's more fulfilling for the people that you have because they feel more challenged and stretched and have the ability to have a very big impact, and smaller organisations tend to be more nimble and flexible to move in directions you want them to go in."