1. Thou shall not regurgitate every fantasy cliche thou hast read in prior works.
2. Thou shall not attempt to overexplain thy magic with psuedo-scientific terminology in am attempt to make thyself seem super smart.
3. Thou shall build an interesting world in which thy fantastical tales may be set.
4. Thou shall not assume that every story is better with princesses.
5. Thou shall avoid overpowering thy characters to the point of ridiculousness.
6. Thou shall not assume that the label of "fantasy" gives thy plot, character motivations, and other story elements an excuse to be unrealistic.
7. Thou shall not follow the path of the Deus Ex Machina.
8. Thou shall not give characters medieval weapons in a modern setting with the sole reason being that it is "cool".
9. Thou shall not pad out thy word count under the delusion that thy fantasy novel must be "epic" in scope and length.
10. Thou shall consult Limyaael's Fantasy Rant List for much better advice than has been provided here.