Structuring your practice
You can just go and 'shoot hoops' but it won't add much to your game. Better to work on the things that you know will make you a more effective player and have measurable goals to help you mark your progress. This stops it getting boring and gives you a sense of achievement as you go along.
The elements of a good session
How long should I spend?
30 minutes hard work is better than a direction-less hour.
Once a week is great; make it twice and you'll double your progress.
Structure
Warm up even if it's just running some gentle lay ups to get your whole body moving. Whatever you do, start gently and build the intensity slowly in order to give your body time to respond.
Consolidate some skills that you can perform confidently. Shooting under the basket, basic dribble moves, passing against the wall.
For the main section, you want to choose one skill and work hard on it for at least 15 minutes, thinking about the body movements and measuring your success.
For the advanced section choose something that's a bit beyond you at the moment and work on it for five or ten minutes. Don't worry about progress here; just doing it will lead to improvements and at that stage you can choose to bring it into the main section of your training and find another more advanced move to work on.
Warm down by choosing something easy with gentle movements. Jogging some lay ups is ideal.
Pace
This is quite important: You need some intensity and you need to be performing skills at game speed whenever possible but you don't want to go flat-out for 30 minutes or you'll lose concentration and accuracy.
Do a set of 10 moves or shots or work hard for five minutes and then break for 2 free throws. At that point, calm down, relax, concentrate, make the shots. This regulation of your activity and your state of mind is also an important skill and a part of your game.
Specifics
You can use the resources below to get ideas for specific practice sessions and apply them to the structure outlined here.
They're only a guide and you'll want to modify them to your specific skill level as well as adding in other things that you're interested in adding to your game.
Onwards and Upwards
Click on the resources below to take you to some more information on how to manage and structure your practice and for specific ideas for drills and skills.