Whether you choose to sit or stand while practicing, it’s important you learn the proper posture to save you from bad technique and back pain.
If you’re planning on joining a band or gigging in the near future, it’ll be ideal to get into the habit of standing and playing. While you’ll eventually be able to make a smooth transition from sitting to standing, for now, you should practice just like you’re going to be playing (otherwise, it’s not very good practice).
Sitting down and playing requires an armless (and possibly backless) chair so that you have plenty of mobility. Rest the bass on the knee of your picking hand, and position it so the neck is slightly elevated. You might want to use a foot stool to raise the leg that the base is resting on.
The bass should be flat up against your body. Sit up straight, and make sure you aren’t constantly leaning over the bass to look at the neck. When you practice, glance at the fretboard when you need to, otherwise look at what you’re playing or just look cool. This is important to develop muscle memory, which will make you a much more accurate player in the long run.
You might choose to use a strap when sitting to keep your bass in the right position. Your hands should not have to support the bass at all. If you find the neck keeps wanting to point towards the floor, use a strap to keep it in place.
To find the right strap height for your bass, sit down as describe above. Find a comfortable position, hold the bass in place and then stand up. Attach the strap and adjust the positioning slightly if you need. This ensures that you don’t set the strap height too high or too low for your needs.
When you stand up, you’ll notice that you’re looking at the fretboard from a different angle. Whereas when you were sitting you probably leaned forward to see the fretboard, you can’t do that so much when standing. Make sure to stand straight and keep your arms relaxed.
Handy tip: If you’re going to be standing and playing for long periods of time, pay attention to the weight of your bass when buying. Companies have finally realized the discomfort that 10 pound basses can cause after hours of gigging. You can now find weight relieved basses for that use.