Excellent question! The first thing you have to understand Dragracer is that there is no formula that works for everyone. The best thing to do is to get a coach. If that's not an option for you, buy some books and study the subject. If time restraints etc. prevent that here are some pointers that will get you heading in the correct general direction:
Most importantly you have to consider your age. With every passing decade you will require more rest/recovery between hard sessions. Remember the old saying, 'I'm not as good as I once was, but I'm as good once as I ever was.' That's the bad news/good news truth.
You also need to think about your general level of fitness. If you've been a couch-potato for the past twenty years you're going to have to give your body time to adjust, no matter how fit you were back in the 'old days'. If you're relatively young and still in decent general condition, you can hammer yourself more.
Understand that 'training' includes hard efforts or days, easy efforts or days, and rest/recovery. Training is not just going out and riding midlessly as hard as you can manage.
With the above three points in mind, you should try to 'train' six days a week. Give yourself at least one day a week (but probably no more than two) when you don't get on the bike. If you're really smitten with the bicycle bug this is an excellent day to watch videos, read magazines and work on your equipment.
Begin your regimen with a hard day followed by an easy day. On hard days GO HARD. Finish your sessions exhausted. On easy days go easy. An old Italian put it to me this way: 'just feela da pedal, just feela da pedal.' Your grand-mother should have no problem dropping you, using her 40lb Dutch utility bicycle loaded with 50lbs of groceries. Get the picture? Almost everybody trains too hard on 'easy' days. But these days are important. At a gentle heart rate of say 110-120bpm your muscles get flushed of all waste build-up and your whole cardio-vascular system gets a nice tune-up. The truth is that you reap the benefit of your hard days on your easy days... when you do it right. Ride for at least 90mins. At the end you will feel refreshed and invigorated. You will probably be tempted to do a little 'wind-up' or sprint, just to flex your muscles. DON'T DO IT! Go home, have a shower and get to bed as early as you can.
See how this feels for a couple of weeks. You may think you don't need to recover so often. If so, try two hard one easy, two hard one easy, rest day. The other option would be one hard two easy, one hard one easy one hard, rest day. Getting the idea?
Whatever you do, don't go out and try to push yourself everyday. Also, realize that even when you are tired from training, you will feel better once you get out on the bike and ride for a while. You will then be tempted to 'push it' a little. That's how you dig yourself into a hole.
One final point: Check your HR every morning when you wake up. Get to know what your 'normal' HR is. If your pulse is higher than normal when you wake up, your body needs recovery. Never do a hard day unless your pulse is 'normal' when you rise in the morning. (unless you're in the middle of a stage race... then you have no option)
Hope you find these points helpful. Have fun and enjoy the journey.