It's excellent to be busy, especially if you're self-employed. Being busy usually means that you have a steady stream of work coming in and lots to keep up with. That's good for business, so you've got to work hard to keep up the momentum. Time management is a skill you'll have to master if you want to keep afloat, particularly because you need to figure out how to accomplish today's tasks while still laying the groundwork for future projects.
If you want your professional development to continue, you'll have to carve out time for networking, personal writing, conferences, etc. These things may not pay like the client who's blogs are due by Friday night, but they are an investment. By writing personal material for your portfolio, reading important industry publications, or rubbing shoulders with influential people, you're creating a foothold for the next step in your career.
It's okay if your hours aren't 100% billable; that's a dream world. No one is going to pay you for working on you, but you'll slowly become someone who's time is worth more when the next contract comes. Your business will only grow if you're willing to put some sweat in and work towards results, so get to it!