for hosting a challenge, my best advice would just be to be good about updating your thread and answering any questions you might get. you don't have to make the op flawless and perfectly coded or anything, just organized and easily understandable. some aesthetics are nice (sprites, colors, different font styles to highlight major points, etc) and make the op appealing to the eye, but aren't necessary. here are some of my threads that make ass examples, but should get the point across:
really simple and straightforward
literally only the rules and participants
graphic design is my passion
this one is actually kinda cute
really simple and straightforward
literally only the rules and participants
graphic design is my passion
this one is actually kinda cute