RULE NUMBER 1: ALWAYS THINK TWICE.
I've saw so many fantasy world trying to be "realistic" but then they are illogical.
Better logical than realistic.
RULE NUMBER 2: SET YOUR OWN RULES AND RESPECT THEM.
Avoiding making too many exceptions to your own rules, especially if you don't have explanations for them. If you say that, for examples, elves can fly, but humans no, why should you make a human being able to fly? Find an explanation, or avoid it.
RULE NUMBER 3: HAVING REFERENCES MIGHT HELP!
You have, for example, a species living on a mountain, with very few trees: how they will take care of their deads? Well, in Tibet for example they offer deads to the birds!
So when you are not sure about something, taking inspiration from reality can be cool! Or even from other fantasy worlds!
RULE NUMBER 4: TO BE COOL IT DOESN'T HAVE TO BE BAD.
I saw too many times world trying to be cool just because "they are so hard t