1. Fill the frame
If your shot is in danger of losing impact due to a busy background/surroundings, crop in tight around your main point of focus, eliminating the background so all attention falls on your main subject. This works best with portraits as can be seen below.
2. Rule of thirds
The most basic rule of photography is the rule of thirds. This is all about dividing your photo into 9 equal sections by a combination of both vertical and horizontal lines. With the imaginary frame in place, you should place the most important element(s) in your shot on one of the lines or where the lines meet. This technique works very well for landscapes as you can position the horizon on one of the horizontal lines that sit in the lower and upper part of the photograph while you're vertical subjects can be placed on one of the two vertical lines.