Learn to juggle
Disclaimer: I just recently learned the 3 ball shuffle, and it was hard to find satisfactory information from the web quickly. There were some good sites, but this is a collection of my experiences of how anyone can learn to juggle in a couple of hours. So far, it concentrates on the methods I know of.
What is juggling? 
Juggling is a physical human skill involving the movement of objects, usually through the air, for entertainment.
Forms of juggling 
There are different forms of juggling. You can juggle different kind of objects (balls, pins, knives, torches, anything else, mixtures). You can have different number of objects and move them in different patterns. You can toss, bounce or otherwise move the objects. You can juggle alone or together with others.
Required equipment 
In the beginning, balls or beanbags may be the easiest to juggle. They are symmetric and you can catch them with an open palm of your hand regardless of the ball's orientation or spin. Similarly, you can just toss them from an open palm and no specific spin is required. Basically any balls should do, such as tennis balls, but it might be easier to learn if you follow these guidelines.
- They should not be too large, or you will have trouble holding more than one in your hand
- They should not be too small, or you will have trouble tossing them accurately
- They should not be too heavy, or you will tire easily while practicing and may hurt yourself or break something
- They should not be too light, or you will not be able control the height of the toss
- They should not be too bouncy, or they will bounce away if you drop them
- They should not be too different from each other, or else each has to be tossed differently
That said, any balls will do. The best ones could be small round bags filled with beans, seeds or rice. They are moderately heavy, do not bounce and provide a good grip.
Your environment should be clear enough that dropped balls do not roll under things and can be easily picked up. If you want to reduce fetching bouncing balls and picking up dropped balls, you can stand next to your bed and have the balls drop to your mattress instead of the floor.
Learn to to juggle 
The following tasks are ordered roughly from the easiest to more complicated. It might help if you learn them in order and one at a time in the beginning.
Note: These instructions are mostly for right-handed people. If you are left-handed exchanging left and right should make things slightly easier. Or you can just learn to use your lefthanded by reversing the directions given.
1-ball shuffle with two hands 
This may barely count as juggling (it may not be entertaining) but it is the basis for most of the toss styles and you can always use this exercise to polish your style in the future.
The task is to toss the ball from one hand to the other.
- First, take the stance (ball in the right hand)
- Stand up in good balance (feet moderately apart)
- Take one ball in the right hand
- Keep your elbows relatively close to your body, low arms horizontal point directly forward, the ball on the palm of the hand facing up
- Look directly forward, do not look at your hands or at the ball
- Ball moves from the right hand to the left hand
- Toss the ball in an arc from your right hand upwards and slightly leftwards
- It should reach at least your eye level, slightly left from your center (nose)
- Catch it with your left hand without reaching upwards
- Return to the stance (with the ball in the left hand)
- Return your left hand to the original position
- Ball moves from the left hand to the right hand
- Toss the ball in an arc from your left hand upwards and slightly rightwards
- It should reach at least your eye level, slightly right from your center (nose)
- Catch it with your right hand without reaching upwards
- Return to the stance
- Return your right hand to the original position
- Repeat from 2)
Practice this until you can toss the ball between your hands sufficiently many times without dropping the ball. For example, when you can make three consecutive series of at least 50 tosses. The numbers are arbitrary, you can always proceed further and return later to polish your basic technique.
These are important things to concentrate on
- The tosses should be similar (arc, height, landing position) from one to the next (repetition and catching are easier)
- Occasionally stop see how much you have to move you catching hand when you move it back to the original position (are the tosses similar and accurate? if you are throwing many balls, you must have economical movement and accurate tosses as time is limited)
- Do not reach upwards with your hand when you catch the ball (economical movement)
- Look directly forwards or even a little upwards, not the hands or the ball (in the future you will be managing many balls and you cannot concentrate on just one)
- Do not let the ball roll of your fingers, toss it up from your palm (it will be easier to control)
- Eyes closed (if the tosses are accurate and consistent, you do no have to move your hands)
- Different heights for the toss (from vertical tosses to ones that touch the ceiling)
- Different style balls (size, weight, can you do it with a balloon?)
- One ball with one hand (toss directly upwards)
3-ball shuffle 
There is only one style toss that is being repeated alternately with the right hand and the left, and the throw is the basic toss from one hand to the other. The heights of the arcs should be equal. At this point do not care if the balls collide in the air. Just start again.
The starting position is the standard stance with two balls in the right hand and one ball in the left hand.
These are the tosses. Next is how you should learn them.
- Starting toss, toss the 1st ball from the right hand (not part of the pattern)
- Toss the 2nd ball from the left hand when the 1st ball reaches the highest point of its arc
- Catch the 1st ball with the left hand
- Toss the 3rd ball from the right hand when the 2nd ball reaches the highest point of its arc
- Catch the 2nd ball with the right hand
- Toss the 1st ball from the left hand when the 3nd ball reaches the highest point of its arc
- Catch the 3nd ball with the left hand
- Toss the 2nd ball from the right hand when the 1st ball reaches the highest point of its arc
- Catch the 1st ball with the right hand
Can you detect the pattern after the starting toss in the instructions? The pattern (left:toss-catch, right:toss-catch, left:toss-catch, ...) is easier to learn in steps.
Starting from the starting position and doing first only the first toss-catch (practice steps 1,2 and 3). In the beginning, you can let the 2nd ball just drop. If you can, you can catch it as well (it is step 5, but its easier when you don't have to pick up the balls from the floor). Practice, starting from the starting position, until you can do the first three steps almost always.
Then, try to add a second toss-catch (practice steps 1,2,3,4,5) and repeat until you can do it almost always. You can also do step 7 if you can make it.
The process is similar to the rest of tosses: add one more toss-and-catch, repeat until you can almost always do it. Remember to stop after you have made the correct number of tosses-and-catches, then start again from the starting position.
If you add the extra catch as soon as you can, you won't have to pick up dropped balls all the time. At some point you might notice that you are back in the starting position with two balls in the right hand and one ball in the left hand. After how many steps does this happen? After adding a few more tosses, you might notice that you are doing the repeated motion of "pumping" or doing little circles with your hands. Now you should get some sense of the rhythm of juggling and you no longer have to concentrate on individual movements.
Colliding balls can be avoided easily when the throws are accurate and have similar heights. There is no need to have every second throw be higher or keep one hand closer to your body. There are two main patterns in the 3-ball shuffle to avoid collisions. The perhaps easiest one is to always toss under the ball you are going to catch next with the same hand. It is possible because the arc of the ball is not quite symmetric, the highest point of the arc should be closer to the catching hand than to the tossing hand (perhaps of wind resistance) Or if the tosses are not that accurate, make the toss a little longer so that you have to move your catching hand outwards (left if the toss if from right to left). Remember to move your hand back to the original stance before tossing again. The other main pattern is to always throw the ball over the incoming ball. If you want to exaggerate the movement in this case, you can make your tosses little short so that you catch the balls closes to the center line of your body.
Note: It can be claimed that the 3-ball shuffle is easier than most 2-ball patterns, for instance, juggling two balls with one hand.