When you have worked as long as I have as a freelance illustrator you are faced with constant challenges.
The most important challenge is the most obvious one: How to attract and keep new clients. Finding and fitting the pieces to this puzzle vary for each individual artist. I know some who have had great success with an agent. I know of others who bought ads in national directories and had tons of work come in from that.
What has worked best for me has been a combination of a couple of methods. The most successful tactic I have used has been precise, individualized marketing. When I have selected a very specific client and focused my marketing efforts towards them I have more times than not landed them as a client. Usually this entails sending specific illustrations from my vast reserve of work that specifically looks like something they would use. Sometimes I even create an illustration that the potential client won't have any problem imagining being used for their purposes. This separates me from the crowd of creatives trying to get this client's attention.
Direct mail promotional pieces have worked well for me also. There are so many great digital promotional printers now. I can very easily design and illustrate a specific, targeted piece for one or just a few potential clients and get a short run of that same piece.
Just because this way of solving the puzzle has worked for me doesn't mean I'm not looking for new ways in the future though. My presence on the various social media platforms has brought me new work and clients also. This is a relatively new way of making that puzzle all fit together that excites me going forward.