This is a link to a Steve Nash video. The dribbling, shooting and defensive drills can be done alone. Obviously passing you'll need a partner.
Defense can be broken down into on-the-ball situations (where you are guarding the ball handler) and off-the-ball situations. Off the ball situations are difficult to train on your own because most of the skill comes from reading how a play develops. One of the best ways for you to train off-the-ball situations by yourself is to watch a lot of basketball and start paying attention to what the defenders not guarding the basketball are doing.
On-the-ball defence is a little easier to practice, even without someone to compete against....and here's why. The key to being a good defender is being able to stay and move in a low defensive stance without getting out of control. This is easier said than done because a good offensive player is going to do everything they can to get you off balance and out of your stance.
Training to be a good defender on-the-ball comes down to training your stance. Depending on what level you are at, you may want to start with just standing in a good defensive stance:
Next you want to practice being able to stay in this position for longer periods of time. Once that's comfortable, practice moving in your stance and never coming out of it. Now add quick changes of direction. Are you still able to stay in your stance, without any unnecessary movement or "buckling" of your upper body? Once you can do this practice:
Remember to always stay in your stance, keep a strong core and keep any unnecessary upper body movement to a minimum.