After startups raise money, their next biggest problem becomes hiring. It turns out it’s both really hard and really important to hire good people; in fact, it’s probably the most important thing a founder does.

If you don’t hire very well, you will not be successful—companies are a product of the team the founders build. There is no way you can build an important company by yourself. It’s easy to delude yourself into thinking that you can manage a mediocre hire into doing good work.

Here is some advice about hiring:

Spend more time on it.

The vast majority of founders don’t spend nearly enough time hiring. After you figure out your vision and get product-market fit, you should probably be spending between a third and a half of your time hiring. It sounds crazy, and there will always be a ton of other work, but it’s the highest-leverage thing you can do, and great companies always, always have great people.

You can’t outsource this—you need to be spending time identifying people, getting potential candidates to want to work at your company, and meeting every person that comes to interview. Keith Rabois believes the CEO/founders should interview every candidate until the company is at least 500 employees.

In the beginning, get your hands dirty.

Speaking of spending time, you should spend the time to learn a role before you hire for it. If you don’t understand it, it’s very hard to get the right person. The classic example of this is a hacker-CEO deciding to hire a VP of Sales because he doesn’t want to get his hands dirty. This does not work. He needs to do it himself first and learn it in detail. Then after that, he should lean on his board or investors to give him opinions on his final few candidates.

Look for smart, effective people.

There are always specifics of what you need in a particular role, but smart and effective have got to be table stakes. It’s amazing how often people are willing to forgo these requirements; predictably, those hires don’t work out in the early days of a startup (they may never work).

Fortunately, these are easy to look for.

Talk to the candidates about what they’ve done. Ask them about their most impressive projects and biggest wins. Specifically, ask them about how they spend their time during an average day, and what they got done in the last month. Go deep in a specific area and ask about what the candidate actually did—it’s easy to take credit for a successful project. Ask them how they would solve a problem you are having related to the role they are interviewing for.

That, combined with the right questions when you check references, will usually give you a good feel about effectiveness. And usually you can gauge intelligence by the end of an hour-long conversation. If you don’t learn anything in the interview, that’s bad. If you are bored in the interview, that’s really bad. A good interview should feel like a conversation, not questions and responses.

Remember that in a startup, anyone you hire is likely to be doing a new job in three to six months. Smart and effective people are adaptable.

Have people audition for roles instead of interviewing for them.

This is the most important tactical piece of advice I have. It is difficult to know what it’s like working with someone after a few interviews; it is quite easy to know what it’s like after working with them

Whenever possible (and it’s almost always possible), have someone do a day or two of work with you before you hire her; you can do this at night or on the weekends. If you’re interviewing a developer, have her write code for a real but non-critical project. For a PR person, have her write a press release and identify reporters to pitch it to. Just have the person sign a contractor agreement and pay them for this work like a normal contractor.

You’ll get a much, much better sense of what it’s like working with this person and how good she is at the role than you can ever get in just an interview. And she’ll get a feel for what working at your company is like.

Focus on the right ways to source candidates.

Basically, this boils down to “use your personal networks more”. By at least a 10x margin, the best candidate sources I’ve ever seen are friends and friends of friends. Even if you don’t think you can get these people, go after the best ones relentlessly. If it works out 5% of the time, it’s still well worth it.