We need to see what you have now before we can really help you, can you please post 3-4 pictures?

Ardhendu, It depends on the overall size of the property and also the location. 12x12 could be ok as the guest room but it may be called smaller when it's a master bed room. Thanks, Nitin Cornerstone Designs, Bangalore.

It's very open ended question , pls share floor plan, pics and requirement details to get a better estimate.

Arshi, there are hundreds of way to decor.  Start with defining your requirements and appropriate budget to get meaning ful answers