Is there anything called GUI standards?

Question

GUIs are one of the important areas in most of the software products. I would like to know whether there is something called GUI Standards that defines the best practices in GUI

Answer 1

Use your users as a standard. What works best for them is what is best, so talk to them, show them prototypes and use their feedback as input to the final product.
Have a look at Jakob Nielsen's Website for a wealth of usability material.