Start out with a miserably textured and lit room that you used a tutorial for every step of like everybody does. You're probably going to be so proud of it, but don't delude yourself into thinking it's good and never show it the light of day. Read more tutorials, make a second map, post that one. Get horribly berated by insults and negativity. Read more tutorials, improve what people said sucked and make a third. Post that. Repeat this process until you stuff out a map that with any luck will be mediocre. This can take months.
That's the reality of mapping for you.
