IntCks have no single "correct" formula. It depends a lot on setting, what level RP, whether its a new or old RP, what sort of players you seek, and of course luck. It doesn't matter how good an interest check is if the players looking at the time aren't the sort you seek.

What an interest check in general needs is something to catch the eye of the prospective players. A stylish image (again, a matter of opinion) can help here.

We also find hiders to be useful to keep it short-looking initially. Headers tend also to help. And sometimes, so too can colors.

Finally, don't give up on one. The one we're currently operating did not have blatant effects the first couple of days.