Keep it simple. This is golf. There is a fuzzy boundary between golf and a real program. Detailed specs definitely cross that boundary.

Be sure there is a solution. Even if you don't show it, the mere act of writing your own solution will clarify questions and make sure that your problem is doable. There is a fine line between problems with minor tricks and NP-complete brute force searches.

Two solutions are even better. If you can think of at least 2 ways someone might reasonably approach the problem, then the golfing course is likely to be more interesting.

Drop boundary cases if possible Often careful handling of boundary cases takes more work than the main algorithm. The main algorithm is usually the more fun golf challenge.

Wait before posting Too many golf problems dilutes all of them. Wait until nobody else is posting problems, then post yours.