It's not hard. Just takes time, patience and a good look at your picture's background.
The first thing you need to do is marquee around objects/people you don't want to be affected by the cloning. In this case I want my mother and granddaughter to remain, while I want to get rid of the people and car just behind their heads. I will use the lasso marquee tool, set to point to point (I'm just not that good at freehand). I am only going around the areas of their heads that would be affected by the clone. Why make more work than necessary, right?
After marqueeing, go to Selections>Modify>Feather and set the feather at 2.
Next go to Selections>Invert.
Zoom in close, real close. Choose your clone brush, set the size and we are going to work it just like we did on the scratches. The "+" hatch (B) is the brush and also is used to set the area you are copying from. The "x" hatch (A) will show you the areas you are copying from as you use the brush.
Just to reiterate, "A" is the area I am copying; "B" is the area I am covering up.
It is important to remember to constantly copy and clone from different areas near the area you are trying to hide. Otherwise you will end up with my results below. As you can see it looks like all I have done is copy and pasted.
You want your photo to look natural. Bottom line is:
1. Take your time.
2. Study your photo.
3. Determine what areas need to be copied so the photo appears natural.
4. Small steps.
5. If you have objects or people near the area to be cloned that are not to be affected marquee around them, feather and invert.
6. Zoom in and out often, so you can see how it is looking.
7. Have fun.