Whenever I read and learn about new technologies, I want to sit down and write programs that help me solidify the concepts better. I'm still in college finishing up my CS degree so I don't know if this is a sustainable way for me to stay sharp. Are there better ways to improve or is prototyping a good practice in the professional world too?
Projects. Real implementation of something. That's the generally-agreed-upon-definitely-best way to improve your skills.
If you find a technology that interests you, try to implement something very basic using that technology, and build up from there. Solve problems with the technology.
Another fantastic way to grow as an engineer is by contributing to open source projects. Find some low-key libraries for your favorite language and help solve issues, etc.