I'm far from a 'serious' rider, but I spent the last winter on the trainer working on spinning at 90. Trainer's not quite real world, but when I could do a solid hour at 90 rpm in the big chainring and 2nd smallest cog, I went and tried in on the local path. Big difference. Of course, dropping an extra 20 lbs over the winter didn't hurt, either. Making the change from clips and straps to clipless added about 2mph to my average pace as well.

I'm still a wimp on hills and need to do some serious climbing drills if I'm going to get better and reach my goal of being able to do a 300 mile tour, but working on cadence worked for me.