This depends on what you want to do. Web development can be anything from installing Wordpress with themes, which can be done by one person with little skills, to large complex sites with teams of people with a wide array of specialties (Facebook for example.)

The money tree starts with the guy who lands the gig from the client. That guy will then either do everything himself (or with an in-house team) or do some parts and then parcel out the rest to other contractors. If you can sell, the you don't even necessarily need web development skills. You can simply land the gigs and sub-contract out everything. Sub-contractors could even hand work out to more sub-contractors.

Where you get work depends on where you fit within this scheme. As a CSS / HTML / Jquery guy you are considered a "front-end" developer. Note that that doesn't make you a designer or a UI guy. Those are totally different areas which you haven't mentioned. CSS / HTML / Jquery has NOTHING to do with being able to deliver good designs. You are simply a coder. You will likely be handed all your designs.

If you aren't doing the selling at the root of the money tree then you somewhere along the sub-contractor track. However, you still need to be able to sell. You still have a client. Your client is going to be another developer.

Now that you know who your customer is. You now need to locate that customer. The developers you will be working for can be anywhere along the money trail. They might be agencies which generally handle marketing strategy for the client and directly sub contract out all the parts. They might be development shops which receive designs from the agencies and handle all the building. They might be solo designers who do generally do as much as they can but hand certain parts off when they are overworked. I have worked with all of the above.

All these people will likely be hanging out in places such as CMS forums, web development forums and social networks such as Twitter. They talk to each other to get help with what they are doing. For example, if they need Jquery help, they will go to a community where they can get help on Jquery. Aside from help, they will also go to places where they can discuss general happenings in the industry. If they are passionate about Jquery, then they may show off things they have done in Jquery. If they are unhappy about the direction of Jquery, then they may want to talk about that. You get the point.

Your job is to start locating these various communities and participate. You need to help people, engage in conversations and show off things you have done. Collectively this process is building your authority. It's a PR game. The more people see your face, the more they hear you talk about intelligent things, the more of an authority you will become. Eventually you will start to receive offers to do gigs for people.

Once you start doing work, then you are building a network. Your network is your bread and butter. The larger your Rolodex, the more secure your future. This is where your work will come in from in addition to all the above mentioned activities. As you bring in more work from your Rolodex, you can do less of the other stuff, but never quit. I have at time worked with certain developers almost exclusively for periods and I have been in totally new ground for periods. I have found that for me, always exploring new ground is better for building those networks.

To do everything described above, you need something to stand out. Just being an HTML / CSS guy isn't very sexy. How are you going to show that off? Your personal projects and portfolio (this is the portfolio you have before you are really even getting work) needs to be pushing the envelope a bit. Developers specializing in nothing but spitting out HTML / CSS are a dime a dozen. There is a lot of noise there to overcome. As you get closer to the bleeding edge, you have less noise. Become and expert there.

What's leading edge? I don't specialize in those areas so you might know better than me. Know HTML 5, CSS3 and all the other related buzzwords that you see in Hacker News. In the JS (Jquery) world there is a lot more you can do to impress. You can build Jquery plugins, become expert with building apps in Node (then you get into server side programming which is a whole different ballgame) and work on building great UI's. You could also begin to specialize in things like UI or design if you see something you like better.

Also keep in mind that this is all a business. Customer managemment, business management and sales are all more important than the technical skills. This is a long and stressful track, just like any business. Make sure this is something you really want to do. Contract developer is sort of like restaurant owner in that it's an idea that everyone comes up with. There are so many other businesses you can get into that you can do totally online that would likely be more interesting and likely more lucrative. Consider this, you aren't likely to ever get rich from doing web development for other people. The people with the great chance of being rich is the people you are building for, the client from which the money tree grows. ;)