How Do You Design Dungeons?

This is a question I hope I have never asked in past. So how you design your dungeons (and megadungeons in particular)? Do you just draw, draw, draw and then add encounters using the random tables (i.e. monster, empty, empty, trap, monster & treasure, empty, empty...) or do you place each encounter as you see fit? Or a combination of both? Or maybe you decide on the general feeling of the level before you even start mapping? And where do you write your notes? Do you have a notebook? Or use a computer? Or directly write stuff on the map?

I would be glad to read everything about your dungeon design methods, and especially your tips for dummies if you have some to share!