Guidelines for when to use Static class over instance class? [duplicate]

Question

Possible Duplicate:
When to Use Static Classes in C#

Can someone please provide guidelines , standard checkpoints on when to create static class and when to create instance class.

Basically many a times I see while writing a code that the same thing could have been done using static class and methods and i get confused with many things.

So far i know below check points :

1. If object under the consideration can exists only once in entire application then it would come under "static"

2. If a method does not use any field variable inside it then it can be static method.