When to train again is probably the greatest factor in getting fast. We get stronger and faster from hard workouts, but do too much too soon, and you will burnout physically and mentally from overtraining.
Growth or "supercompensation" from previous workouts only takes place when complete recovery has occured. Train too soon and you will start digging yourself in a hole that will get worse the more you do it.
Disinclination to train, irritability, insomnia, depression, poor appetite, etc. are some of the signs of overtraining.
Everybody is different. Some people can absorb and recover from incredible workloads, others cannot without protracted recovery periods. You must know your body and its limits. This will take time to figure out. Keeping accurate training logs will help you assess your progress. If you get overtrained, go back over your logs for the last month or so and look how much intensity work you have been doing.
Nobody can tell you when to train again. You can work the soreness out of a muscle with exercise, but you cannot work overtraining out of a muscle with more exercise. You can be sore and not be overtrained.
Sometimes, riders will train in blocks of 2-4+ days hard in a row. The idea behind this is to train hard with tired, fatigued muscles,which forces the body to recruit additional muscle fibers that would otherwise go untapped. The more motor units you can recruit, the faster you will go. Most people don't train this way however.
Lots of pros say they don't get to really high levels of fitness until they "crash" to a higher level through short periods of overtraining. this might be 5-10 days or so. Day after day of muscle soreness, fatigue, big miles and hard efforts. After they recover from this overtraining, they "crash" to a higher level. You must really know yourself and what you are doing when training this way.
Most people do too much intensity work at a time in my opinion. Classic workout examples are 6 x 4-5 minute intervals, twice a week. Some people can recover from this, but I think a lot of top riders can't but still try.
If you only did one or two 5 minute intervals, chances are you would be 100% recovered two days later. It would be less time on the bike, less mental stress of pushing, etc. If you did one or two intervals on tuesday and were 100% recovered on thursday, you would make consistent improvement on a week-to-week basis. You would be stronger and faster every week!!!
Recent weight training studies in the last few years have shown that doing one set of exercises in the gym gives about 90-95 of the benefit of doing 5 or more sets!!! You get your workout done a lot faster too!!!
If you stick with 6 intervals on tuesday and try again on thursday, you might only be 90% recovered or less. After the first or second interval your performance might drop off. You will start feeling like a failure for not accomplishing your workload. Negative feelings and thoughts breed like gasoline on a bonfire in this environment and are very detrimental for a competetive riders confidence.
These are just examples. Everybody is different in their ability to absorb and recover from hard workouts.
Consider overtraining yourself a little to see how much it takes and what it feels like. Get yourself well recovered. Then try riding 5 days straight with 80-100 miles a day of hard riding. Do lots of climbs, chase down and attack other roadies you see on the highway. Refuse to be caught or dropped by others. If there are no roadies out, chase down cars or buses. Drag race cars from stop lights and see how long you can hold them off before you crack. Blow yourself up, recover, and blow up again. Repeat many times.
Visualize you are riding in the Tour and you are on an 80-100 mile solo break. Don't ride slowly at all except to warm up and cool down. Explode yourself every day. This is what I have done in the past. I noticed a big increase in fitness once I recoverd, but I suffered a lot while doing it!!! Again, this kind of thing is highly individual. Your mileage may vary.
A pro might have to do 150-200 miles a day for this to be effective. Training like this is not for everybody. Experiment. Learn what your body is capable of doing and how far it can be pushed.
As for recovery, ride your bike easy. You can take a day or two off the bike, but your muscles will get stiff because they will shorten as they grow and get stronger. Stretching can help, but you can really injure yourself by stretching too much or too hard. Ride 30-90 minutes in the small ring at a low cadence and slow speed. The pace should be so slow that you feel almost ridiculous riding at that pace. Stay on the flats, don't do any hills. This means 60% or under of max heart rate. Lot's of pros only go 12-13 mph when doing these rides. Some pros are different. I remember reading that former Dutch pro Adri Van Der Pol's idea of recovery was a 4 hour ride on Mondays!!! In the off season, when most riders take a few weeks off, he used to run for an hour every day!!! Everyone IS different!!!
Only time and experience can guide you to the proper balance.