[1] Do not post ridiculously overpowered races; they're not welcome and not needed. Balance them and post them to learn from them. This site is an excellant place of knowledge.
[2] Try to be as original as possible. It is understandable that you can only do so much with a C&P race and with your limited knowledge, however there do not need to be 20 ninja races or 7 super assassins.
[3] Only post races you put some thought into and actually tried on. Don't post something you threw together as a joke or admin race for your server.
[4] If you would like help on your race or would like to know more about making races, be respectful and maturely ask for help. Noobs will be ignored.
[5] Add your ideas behind your race to your topic or possibly come up with an idea of why you made it to make it more personal and more distinct. Creativity is everything.
[6] Don't spam races. Learn from the races you're making so you become a better coder, instead of spamming race after race.
[7] Make your skill descriptions accurately describe the skill. There's nothing worse than not knowing what a skill does.
[8] It is perfectly fine to copy a skill (or skills) from an existing race, but it is never okay to try to copy a whole race and claim it is your own.
[9] The best way to learn is to look at preexisting races and to ask questions based on what you don't understand so you can learn to use them in your own races, instead of blindly asking questions with no previous knowledge.
[10] Some of the most common errors are misspelled words, incorrect syntaxes, or improper command "puncuation" (such as forgetting quotations, too many spaces, etc.). Always look for those first if something isn't working.
[11] Always post your races neatly. Have the coding itself neatly written and posted in the code or Eventscripts code form for easy viewing and help.
Please post more ideas!