How do develop a side project when you have a 40hr/week job?

I am a developer and I have a 40 hr/week job. It is a very good job and I put a lot of effort in it. But I have also my own ideas that I would love to develop, but I am struggling to organize time and material to develop something for me. I read a lot and have a lot of ideas, about little porjects to test new technologies or new patterns, but never find the time. I would love to learn the experience and techniques used by someone who have been able do to something like this.