Couple different things, not really having to do with fitness per se (I won't tell you to go 30 seconds hard or whatever). First is what I termed Maximum Optimum Sprint Speed:
http://sprinterdellacasa.blogspot.co...sprinting.html
Basically what you're doing is getting a pretty repeatable and consistent fast sprint in. I've seen friends/teammates go from 30-31 mph to 40-41 mph in 2 months. One guy was a super skinny, climber type rider who couldn't sprint to save his life. He ended up a phenomenal leadout man. Some will be going faster. To put things in perspective if I'm seated and not doing an all out sprint I can do a 35 mph pull, depending on the wind. This is long before I actually try to sprint. I'm not "fast" per se but I can go hard if I need to go hard.

Go to about 10:00 to set up for a 35 mph pull. Go to about 14:00 for a sprint.

Another thing you can do is race, do fast group rides, or motorpace. They all do the same thing - they give you a chance to draft at speed. This really improves your speed because you can work at a much higher level but with smaller deltas. For example in a variety of races I'll be doing 35 mph on flat roads due to certain variables - slight downhill before, protected from wind in general, etc. I can accelerate within the group from 35 to 38 mph and not use a lot more energy - I might be able to sustain the higher speed for 30-45 seconds and then "slow down" to 35 mph without going into massive oxygen debt. However if I was going 35 mph on my own it would take a huge effort to go to 38 mph, and in fact I'd blow up within 30 seconds or so. The idea of making low level effort changes (relatively speaking) at high speeds is what makes training while drafting so useful. This means you can fluctuate your speed without constantly blowing yourself up. This in turn means you can hold a very high level of effort for a longer time.

You can also do cadence specific work. The 120 rpm average thing is good. Keep in mind that longer cranks means lower cadence. I could do 120 rpm on 170 mm cranks, with a lot of effort. On 175s I'm more like 105-110 rpm. My cruising cadence is about 105/100 for 170/175 mm cranks respectively. I push at 80/85 rpm.

I'll do max rpm efforts on a mostly unloaded resistance flywhel unit. In the clip below I'm on 175s and hitting 235-245rpm. On 170s I've done 285+ rpm but haven't seen that in a while. I'm guessing I'd be able to hit 255 rpm, maybe 265 rpm. Doing this a few times a week (3-5 efforts, no more than 10 seconds each) will let me improve my max cadence by about 20 rpm in 6-8 weeks.

First part of the clip below shows three efforts on the flywheel thing (I was checking position and in particular my knee for any weird movement, hence the angles).

Finally you can go out and do really, really long rides. I get criticized for doing 5-8+ hour rides when I primarily race hour long crits. The long rides aren't necessarily for the crits per se, they're to try and force my main cycling muscles to exhaustion. Just like you will go out and use a lot of energy when you're fresh, you can also use that energy to mask pedaling deficiencies. After 3-4-5 hours you're fatigued, sore, and you tend not to flagrantly waste energy. This means pedal deficiencies start to surface. I find myself tilting my pelvis, not flexing my ankle as much, flattening my back, etc. Do rides like this while focusing on pedaling smoothly and a lot of stuff becomes automatic. I had one guy comment on my pedaling style while we were bombing through some single track in the woods. He was amazed that I could pedal smoothly. It wasn't that it was a gift or anything - I worked at it really hard.

In another life I was a much better violin player than I ever was as a cyclist. There were two reasons why I was good at the violin - I had good intonation (I made the right tones) and my teachers drilled technique and form into me. The latter allowed me to maximize my potential because I wasn't doing stuff like holding my violin up with my left hand (you hold a violin up with your chin, freeing your left hand so it can move around quickly and smoothly), grabbing the bow with a crushing grip (such a grip prevents you from using the bow in an elastic manner, killing your tone), etc. When I started cycling, maybe 5 years before I stopped playing violin, I realized that the technique drills applied to both. Therefore I went and did technique drills on the bike, even as a kid. I understood just how much they help in the long run.