More Spinning Mistakes

Rocking and swaying on the bike:  If you are moving your torso all over the place there is no way you can ride in good form. 

Pushups on the handlebars: There is not enough resistance for this to be an effective move.  All this does is increase the amount of forward flexion.

Riding with one or no hands:  This can be dangerous, especially while standing or jumping as your foot could slip out of the pedal.

Dropping the seat in the middle of class:  If your seat is set up correctly why would you want to do this?
Very high resistance:  This may be ok for very brief intervals, but pedaling at a super slow level will cause you to squeeze the handlebars and can lead to strain in the upper body.

Very low resistance:  Not only will you get little benefit, but pedaling at a very high speed can cause your foot to slip.

Pedaling backwards: Most Spin bikes will be damaged by this move, and it really makes little difference to your muscles.

Jumps:  These are controversial.  Most fitness experts believe jumps can be safely done in an indoor cycling class, but there are some who believe the risk of injury outweighs the benefits.  Know your fitness level and avoid jumps if you are new to Spinning or have any joint problems.

Exclusively Spinning: Indoor cycling is a great workout, but it is not enough by itself for a balanced fitness program.