I just want to share some knowledge and give some tips on mapping. This is for novice mappers as well as for people that are already familiar with Cube editing. For learning the basics of how to edit maps, refer to the readme.html.
Some opinions on certain topics might be influenced by my personal taste and views. I don´t claim this were the ways to do it, but it´s the way I do it and what I find important.

Since I have never made a singleplayer map (I like multiplayer better) I can only talk about making multiplayer maps here.
I will divide this into sections, which are

1. Layout/Performance
2. Gameplay
3. Design (detail, mapmodels, light and stuff)

1. Layout/Performance

Starting a new map, it is always good to have some basic concept or idea in mind.
Sometimes I will just start mapping and develop ideas as I go, but often I have an idea, and I will take a piece of paper and get it down first. (sometimes stanze aka lahme, my beloved girlfriend came up with sketches too ;)