Steve Jobs' black turtleneck sweater was famous. Mark Zuckerberg has his own uniform of grey T-shirt and hoodie. Both built enormous companies that made them billionaires. But you have to think there's more to their success than the ability to lose the two minutes a day wasted picking shirts.

In fact, Mark Zuckerberg has four productivity techniques that enable him to get more done each day and reach the kind of goals that for most people remain a dream.

1. Focus on the work... all the time.

In a Q&A on Facebook last year Mark Zuckerberg was asked how many hours a week he works. He hedged. "If you count the time I'm in the office, it's probably no more than 50-60 hours a week," he said, but added that "I take a lot of time just to read and think about things by myself... if you count all the time I'm focused on our mission, that's basically my whole life."

That sounds like a fudge but there's something to it. How often have you walked down the road humming a tune or replaying a conversation that's already happened? How much more could you achieve if you spent those moments planning your project or anticipating the actions you need to take when you reach the office?

At college, we quickly learn that the preparations we make outside the classroom are more important than what we learn in it. When Harvard dropout Zuckerberg takes the same approach to quiet moments outside his office, he makes those office hours much more productive.

2. Set annual goals.

Despite his claim of laser-focus, Zuckerberg has always had interests beyond social media. But the way he manages those interests is telling: he gives them annual goals.

In 2010, he set out to learn Chinese. The next year he committed to eating only meat from animals he'd killed himself. In 2015, it was to read a book every two weeks, a project that he opened to everyone with a community page on Facebook.

Self-improvement is always a good plan but instead of squeezing it into whatever spare time he had available, a recipe for never doing anything, Zuckerberg applies the same degree of focus and discipline that he brings to the workplace. It makes that improvement much more likely to happen.

3. Just get moving.

In his book Mark Zuckerberg: 10 Lessons In Leadership, Michael Essany quotes the founder of Facebook as saying: "I think a simple rule of business is, if you do the things that are easier first, then you can actually make a lot of progress."

That's a pretty simple philosophy and it's common for Silicon Valley firms to ship "minimum viable products" to test the market rather than waiting until their new gadgets are completely polished and full of features. But Zuckerberg is on to something bigger.

Doing the easy things first creates momentum. It teaches lessons and keeps you moving forward. Nothing gets big things done faster than getting the small things out the way.

4. Keep your employees sharp.

Steve Jobs wasn't just known for wearing black turtlenecks. He was also known for being extremely tough on his staff. Incompetence wasn't tolerated and his comments could be withering.

In his account of the early days of Facebook, Noah Kagan describes Zuckerberg's reaction to receiving poor work. He threw water over an employee's computer when a demo didn't impress and threatened to use a (fake) Samurai sword to decapitate anyone who took the site down.

That kind of behavior might have not come from any employer's handbook, and probably had more to do with immaturity than smart management, but being tough on employees and making clear that you're not prepared to accept shoddy work will keep your staff on their toes. It's never enough for you to be productive; you have to keep the people under you productive too.