Creating a keyword map

How does it work exactly?
Read a couple of threads and still confused.
Do you take all keywords and place them in categories or do you take one keyword and place several others around it?

eg:
Weight loss:
lose weight fast
lose fat quick
quick weight loss tips
weight loss diets
healthy weight loss diets
...

or

Weight loss tips:
Quick weight loss tips
Fat loss hints
Weight loss diets:
healthy weight loss diets


It's my first time ever doing this and I'd like to do it good