If you are between jobs then I encourage you to take advantage of all this wonderful free time. It is easy to get discouraged and then start watching TV and hanging out at the gym/bar/bike shop. Don’t! This free time is a rare gift. Use it to exercise your skills and create something.
Be disciplined about it. Get up early every morning, shave, get dressed, and “go to work” on your own project. Don’t just fiddle around with exercises. Make something specific and concrete that is a finished item you are proud of.
If you are a programmer then make software. There are zillions of open source projects that could use help. If you don’t like working with a team of undisciplined volunteers then make your own project.
If you are a writer then write. You could start a blog on a subject you care about. It’s very easy to start a blog.
Unless you are a fighter pilot, you should be able to hone your skills with those extra 40 hours per week.
Don’t worry about choosing a project that will impress an employer. Anything done well is impressive. As an employer, I don’t mind a gap on the résumé if something interesting was happening then. You are demonstrating that you truly enjoy your craft because you do it even when you aren’t paid. You do enjoy your craft, right? If you don’t then for heaven’s sake use this time to find some other calling!
Impressing employers is nice, but there are better reasons to exercise your skills. You will get better at your craft. It’s fun to be skilled and it will make you more confident. The very best reason is that you will make something! You won’t need an employer if your software, blog, cookbook, photograph, art, or gizmo is awesome and it starts making money.