Ceiling fan wobbling? I can prescribe some actions to straighten that out. First, turn the fan off. Sight along the edges of each blade, checking for warping. This is usually not the cause of wobbling, but it's one of the easiest to check. If a blade is warped, you may need another set of blades, but try the Vertical Variance method below first; it may reduce the wobble considerably. Also check for any loose screws connecting the blade to blade-iron and blade-iron to motor (if wobble is accompanied by a "tick-tick" sound). Also wiggle the hanging bracket and canopy and make sure it is secure and not loose. A loose hanging system can can cause a wobble by itself.
Wobbling is usually caused by misaligned blades. And usually the blade irons have been bent. They can bend due to the weight of the blades over time, as well as human intervention.
Vertical Variance (most common, where fan did not wobble before)
Using measuring device (ruler, yardstick, or even a piece of stiff paper and pencil) measure the distance from the tip of one blade to the ceiling. Leaving the measuring device in place on the ceiling, carefully rotate the fan blades (if it is a ball mounted fan be sure not to change the angle at which it hangs) so you can measure the next blade. Repeat with the remaining blades. Most likely you will find one or two blades either too high or too low.
Check the blade irons for cracks, especially near where the blade iron widens to accept the blades. If you notice ANY cracks, do not proceed with the next step; REPLACE your blade irons!
To correct - hold the motor with one hand (the switch cup makes a fair handle for this) gently applying pressure to the end of the blade (either up or down) will straighten the blade iron. Don't overdo it though, too much will weaken the blade iron. Double-check measurements and then test fan under power. This usually takes care of it.
Pitch and Centerline
If it still does not spin right, the Pitch or Centerline Angle of one or more blade irons may be off. The way to test these involves removing the blade irons from the motor and blades. To check the Pitch, hold the bases of two blade irons to a flat surface. With the blade-ends facing each other, the opposite sides should line up. That is to say the upper side of one should match the upper side of the other, and the same with the lower sides. Check all irons this way. To check the Centerline Angle, stack the blade irons together. Holding the stack firmly together at the bases, align them to one of the holes in the bases. Look at the blade ends of the blade irons. They should all be evenly spaced (for pitch) and lined up in straight lines. Unfortunately insufficient leverage prevents a quick fix for these problems.
Excessive Blade Weight (wobbles upon installation)
Sometimes fan blades are not exactly matched by weight. If the weights of the blades vary more than 0.5 grams, the order in which they are attached to the fan can cause a wobble. This would be apparent upon installation. To adjust a 4-blade fan, swap two neighboring blades (1-2-4-3) and retest. Re-try (2-1-4-3) if necessary. For a 5-blade fan, swap opposing blades (1-2-5-4-3). It is a good idea to number the blades with post-it notes and record the combinations tried, as this takes a few tries (1-4-5-2-3, 5-4-1-2-3) in most cases. If this does not take care of it, Blade Balancing Kits are available, consisting of a few 0.5 gram weights, and a way of determining the placement of the weights (usually a sliding 0.5 gram clip).
I've used these methods with much success. Wobble-correction is time-consuming, and it takes longer than it looks. Very rarely is a wobble caused by an out-of-balance motor (I've seen 2). To test, run the fan without blades, if it wobbles severely this may be the case. A slight wobble can be corrected with one of the above methods.