That really depends on the type of job he's looking for.
While it's true that many agencies seem to want someone who may not be absolutely amazing at any one thing, but is instead fairly good at a little bit of everything, that's not the case with high end agencies. They usually have dedicated front and back end teams as this allows them to hire employees that may not be able to do a little bit of everything, but the things they can do, they do very very well.
Source: I'm the senior front end dev for a larger agency
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I didn't even notice that the OP is asking about design, not development.
- First of all, you're going to want to get a good working knowledge of Photoshop. While some designers advocate using Fireworks, PS is the industry standard so learn it first.
- You're going to want to subscribe to a lot of design and development blogs and do a lot of reading. You're going to want to read up on design theory, color theory and typography.
- Start designing websites. If you're stuck for ideas of what to design, come up with your own redesigns of popular websites such as Facebook, Twitter or even OCUK.
- Even if you plan on being a dedicated designer who just hands over the psd's for a front end team to build, I highly recommend learning html/css/JavaScript/jQuery. You don't need to master it or anything, but even a basic working knowledge will benefit your designs as you'll have a better understanding of what works and what doesn't when it comes to actually building the site.