When a really good juggler gives a workshop or class you will often find that rather than reeling off a big list of tricks, which could be learnt from a book or from a friend who does them already, they will concentrate more on the way their students juggle - their body position, degree of relaxation, the symmetry of their movements and their mental attitude towards their practice. These factors are of relevance to anyone who wants to improve, no matter what level they are at; indeed a beginner may benefit more than an experienced juggler from such instruction because they have yet to develop bad habits which may be hard to remove after they have been ingrained over years. I have included below some of the techniques that have proved useful to myself and to others in this area.
I once attended a workshop that focused a great deal on the aspects of juggling mentioned above, and one piece of advice which I was given sticks in my mind as having had a rapid and beneficial effect on the way I juggle. The teacher told me to shift my weight over to the right a little when I was juggling, I was supporting most of my body weight on my left leg. I did as he suggested but did not notice any improvement at first. In order to demonstrate how unbalanced I was, he told me to lift my right leg in the air and stand only on my left - this had almost no effect on my juggling, however when I tried the same thing on my right leg I started wobbling all over the place and had great problems balancing.
Even quite minor changes in balance and posture can have far reaching effects when you juggle. As well as distributing your weight evenly between your feet, it is also important to make sure that you stand symmetrically. Some jugglers, especially beginners, habitually stand with one foot in front of the other. Although at first it may be hard to appreciate how your feet can affect what your hands are doing, you will come to see this more as you progress. Try standing first with your feet in line, relax your body and hold your arms out in front of you as if you were juggling. Looking down everything is level - your feet, your hips and your hands. Now move one of your feet 6 inches forward and relax again, obviously now the lower half of your body is twisted to one side because of your stance, but you should find that your torso has also turned a little. This means that as you face forward your hands aren't level and so your juggling pattern will no longer be parallel to your body plane, consequently you will have to start throwing backwards and forwards slightly as well as side to side, providing more scope for error.
Having one foot 6 inches in front of the other is a fairly easy error to spot, but much smaller distances can also make a difference, and the differences become more pronounced the more your juggling advances. Again this isn't something to worry about when you are just starting off, my advice would be to look out for bad habits forming, but first of all work on keeping the pattern together and then polish up the finer points later.