I also use this technique to clean up acne and other blemishes on skin.
1. When you are ready to start spotting your image, the first thing to do is make a snapshot of your current state. If you hold down the Alt key while clicking on the Snapshot button, you will have the option of naming your new snapshot. I usually name mine something like Begin or Orig.
2. Run the Dust & Scratches filter. Adjust the Radius and Threshold until the spots disappear but the texture of the photograph still remains. This takes some practice to feel comfortable with, but you can do it! I usually adjust the Radius first. then I start adjusting the Threshold in increments of about 5. Once I narrow it down to within a range of 5, I start going through each level until I find the best one. For example, I start with 5, 10, 15, 20, 25, 30... I notice that 25 is not quite enough, but 30 is too much. I then look at 26, 27, 28...
When you find the right settings, click ok and then make another snapshot. I usually name this one D&S.
After you run the Dust & Scratches filter, your entire image will be a bit softer. If you were to just run Dust & Scratches on your image and leave it at that, you'd end up loosing a lot of definition in places like the eyes, mouth, nose and other important features. So, the goal here is to have the best of both worlds.
3. Activate your ORIG snapshot, and point your history brush at the D&S snapshot (by clicking in the small box on the left side of the snapshot). You'll see the history brush icon appear there. Activate your History Brush tool and choose a soft brush set to the smallest diameter that will cover the spots you want to remove. I normally set my brush opacity to about 50%. Position your brush tip over the spots you want to remove and just start clicking. If the first click doesn't remove the entire spot, then use a second click. Setting the brush to less than 100%, allows for different densities of dust spots without having to keep changing brush opacities. There's no need to pick up anything as you do with the clone tool. What you are doing by using this method is replacing small dots of your ORIG layer with the dust free same areas from your D&S layer.
You can also use the Gaussian Blur filter with this method instead of the Dust & Scratches filter. I prefer to use the Dust & Scratches filter, though, because it allows for threshold adjustment. This lets the dust spots be removed while keeping the original grain and texture of the image intact.