[slyall]

So I usually use this site:

http://www.jinchess.com/chessboard/composer/

about once a week for creating diagrams. Have a look at them for some feature ideas.

Looking at your site the main problem I see is you don't indicate which player is to move anywhere.

I don't use all the features on the other site but I think my main advice would be to have a very generic colours and piece-font as your default and give people options to change them.