If you are shooting for accuracy it will be different than if you are shooting drills. Some of the older crowds eyes will wear out long before their arms do (they cannot see the target clearly). You should go out at least twice a week as you will see a difference. As for the amount of time or ammo each outing that depends on you. You accuracy will go down as you shoot because your muscles and eyes will get tired. You can take some breaks and talk with others to rest up and they will come back.
I usually do 100 rimfire and 50 centerfire every Sunday morning to lunch, taking breaks. Then we have action shooting on Thursday, but that is totally different than for accuracy. Sunday is done with accurate firearms like a Smith and Wesson Model 41 and Thursday is with an M & P 9. You can really see how much an accurate firearm plays into shooting well if you own or use one. For example I have often taken people out to shoot, had new members shoot my firearms, and let people shoot who are taking their PAL course. If they use a Ruger 22/45 the groups are not as good as the Smith and Wesson Model 41.
Some say more importantly than range time is dry firing practice. Many people recommend 15 minutes or more a day. This is cheaper and can be done any time you are home. Several books like the Gunner’s Bible tell you to shoot at door knobs and help with your stance and grip. Have someone who shoots Bullseye show you the proper technics and I am sure you will improve as well.
To hold back rest your firearm on the bench in front of you for a count of 10. During this time rest your eyes and muscles and concentrate on getting your breathing right. This will improve your accuracy and have you rested between shots. Do the same thing when you are dry firing to get into a routine you can carry over to live rounds.