Sorry for the long delay, it did take me some time to learn the stuff and apply it thanks to Coop (<3).
Now, after those previous version on how to Set-Up your level correctly, here comes the basic things needed.
Potential
-> Try to keep your walls as simple as possible, and easy to the eye to look at. Don't try to make it too large when not needed.
http://www3.picturepush.com/photo/a/9163151/220/9163151.png (Unsupported image host)
->Pillars can help you around the walls for stars and such stuff, but make sure to use them correctly.
http://www2.picturepush.com/photo/a/9163215/220/9163215.png (Unsupported image host)
->Shading floor tiles would look always nice, but make sure on the way you try to do it, there are several ways. Some people shade it by Light and some others simply gather it around.
http://www5.picturepush.com/photo/a/9163233/220/9163233.png (Unsupported image host)
->Always make sure that you're using the player's view correctly, remember that its x = level spot /2 and y = - level spot/2 ~ well, once placing a table on front of the wall (down) you would have to cut it legs.
http://www1.picturepush.com/photo/a/9163269/220/9163269.png (Unsupported image host)
->Still got some space? Spice it up with some Rugs, decorations, more tables, windows and NPC's!
At the end, feel free to peek in every while and add something you got in mind.
http://www1.picturepush.com/photo/a/9163439/220/9163439.png (Unsupported image host)
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That wasn't a big tutorial, just sharing the stuff with the people who want to learn, anyone is free to correct me or ask me any questions. Credits goes to Coop, for finding time to teach me almost everything needed.
Thanks for reading!
-John