Balance a washing machine to stop vibration during spin cycle ?

You need to ensure that it's level.
You need a carpenter level and maybe a pair of plyers.

You probably have screw in legs/suports. Screw them in or out as needed.
If you have someone to help and slightly lift the front, you often don't need any tool.

There are usualy two on the front, and some older models also have those on the back, but most resonably recent (less than 30~40 years) have a swivel arm in the back that don't need adjustment.
If there are screw legs on the back, ensure they are properly set.

Electro
February 2013