Speed, one of my favorite bike topics came up in another thread. Rather than hijack it, I'll start here.
I've tried training and watched, on Strava, enough of my fast friends to realize I don't have the discipline to stick to a formal training regiment. I also have figured out organized racing is not an option for me without the formal training and way more miles than I care to ride. My goal now is to be able to hang onto our faster group rides. This usually means an average speed between 18 and 21 MPH for 25 - 50 miles depending on day of week.
I commute rain or shine via bike, on these short ~6 mile runs I ride as fast as I can on my heavyish FG/SS complete with fenders. A good day is 18+ MPH driveway to driveway. If I'm not feeling it or still recovering I ride really slow. What I don't do is ride in the mid effort range where most of my previous riding used to be. On Wed and Sat I do group rides with the fast kids, many times barely hanging on.
This approach seems to be working for me as I'm slowly moving up the pack on the group rides.
If you're trying to get faster, what is your goal and how are you approaching it?