LakiSoft, on 12 September 2012 - 12:15 PM, said:
Please someone tell what i should do to be better mapper! Please!

Practice, practice, practice.
And if you have a hard time seeing if the mood, detail and also the gameplay in your maps is good, then ask for criticism.
If you say that you want to become a good mapper and release some maps and asking what people think and what needs to be improved, they will be more than helpful.
Then, before starting a map, I would suggest you write down a concept and a layout so that you don't run out of ideas. A map is usually seen as a whole, not a chain of random ideas. It needs to have an overall idea. Take a location you think will fit Duke and that you like. Then think about the features in it and what gameplay elements fit. (Example: Cinema -> Streets, Box Office, Lobby, Silver Screen ... you get what I mean)
And if you have made a few good maps you can start to line out a full episode with a full story arc and all that.
EDIT:
Oh, and nobody is stopping you from having five or six ideas from maps that you release one by one after each other that might already have an overall story arc and later might be put together to become a full episode (perhaps with improved versions of your single maps).
BUT: You need to have the ideas for your mapsyourself. Making a map is not like being in the industry where the project lead has the idea and the level designer just executes it.