Adding too much dressing
You almost certainly made this salad error previously, either with potato salad or another salad from your repertoire because it is so typical. However, it's particularly simple to overdress potato salad. This is so because potatoes take up a lot of the dressing. As a result, you might desire to use more dressing than is actually required. Your potato salad may feel overly fatty or wet if you use too much dressing, and all that extra sauce may overpower the other tastes you've added.
The simple fix is to gradually pour the dressing into your potato salad to prevent overdosing. Your best option, though, if you unintentionally wind up with too much dressing, is to add extra potatoes. More potatoes may not be convenient to cook and prepare, but if doing so can save your salad, isn't the extra time spent worth it?