Hi Kristina,
This is actually a very good question. There are tons of little tricks you can use to better display your posts here and I'll go ahead and tell you one of them.
When you post an ad (thread), your ad is placed at the top of the list of all the other ads because it's the most recent. As yours sits and as others post their ads, yours gets pushed down because it's older than the more fresh ones that were more recently placed. Now, here's the trick - to keep your ad above all the others, all you need to do is add to it. If you take a look at your ad page, you'll see a space below for people to reply to what you've already written. You can just as easily use that space to add additional content to your existing ad. Perhaps you'd like to add another photo or two. Or, you can offer an update to the previous ad, such as informing folks if one of the puppies in a litter has been sold. Whatever you choose to add to your posting, it will bump it up into the top spot. Just be careful to add something of high quality or it will never make it through our administrative screening process.
I hope this helps!
Jay