How do you smooth out your skin perfectly without having unevenness and wrinkles ?
The biggest “trick” really is to not have to smooth the surface to begin with. A common mistake among new users is to subdivide too soon, getting to a level that is appropriate for fine resolution details without having adequately blocked out the basic forms first. This results in models that tend to be lumpy and uneven. By focusing on the lower levels and dividing only when you can’t take the design any farther with that level of detail, you get a surface that is smooth and even to begin with – no need to do any fixing.
In other words, you wouldn’t try to paint a house until you’ve first put siding on. And you wouldn’t try putting siding on until you’ve got the frame up. And you wouldn’t put the frame up without a good foundation. 
If you’ve made this mistake with a model, you still have things you can do. For one thing, you can drop down to lower subdivision levels and work on them again. You can also use the Smooth brush to fix many problem areas. This will give really good results if you smooth first at a lower level, then step up one level at a time and smooth some more.
Thanks a lot for reply. I will pratice!!