Following on last week's rule of thirds, here is a tip for Lightroom users. When you use Crop and Straighten Tool in Adobe Lightroom, you can display an Overlay. It displays lines over your image to help you crop it.
You can use the Thirds Overlay but there are many others available from the Tools Menu.
You can cycle through them by hitting O on your keyboard. If you are using 2 or 3 of them on a regular basis, you can choose to cycle through only those. There are also guides for aspect ratios if you want your photo to print nice in different format like 5x7 or 8x10.