Nothing. I've seen a lot of posts about people worrying they won't be taken serious because of their low post count, or clarifying that they've been roleplaying for years in spite of said post count, but I've never actually seen anybody treat anybody differently for having a low post count.

In my experience, the best way for getting an interest check attention boils down to two things.

1. Be clear and specific about your idea. You don't have to outright say "It's a quest from point A to point B" but the less vague you are, the better. Having a TL;DR at the bottom sometimes helps.

2. Make the formatting pretty! Centered images, nicely sized paragraphs, hiders, and proper spelling and syntax make people go apeshit. I've seen a few interest checks tank because they're giant textwalls, in spite of being pretty good ideas.