A framing device is a very useful tool in improving your photography. It has been used by artists long before photography came onto the scene. It is helpful for pre-visualizing the final photograph.
For those who use a standard format sensor in the 2 x 3 ratio the best and simplest framing device is an old slide. The plastic ones with white on one side and black on the other make the most fantastic light weight framing devices. We should put them on a neck chain and wear them. As now that they are retro, they would look fantastic...
To use one is simple. Choose the white or black side for your scene. If your shooting in a dark environment choose the white side. If your out in bright conditions the black side is going to be more effective.
Now hold it up to your eye and look around at the world and start taking photographs in your minds eye. Hold it parallel to your eye ball (perpendicular to your line of sight). Hold it 5 centimetres from your eye. If you do this, you now have the equivalent of a 50 mm full frame lens on your camera. Move it out to 10 cm and now you have a 100mm full frame equivalent on your camera. Move it in to 2.4 cm and you have your wide angle 24mm full frame equivalent.
Now practice and practice and practice framing up your photographs in your mind. Notice how that when you move the photograph is going to change. Move closer to your subject, move up or down and reposition objects so that they make a balanced composition. How do you know it is balanced, well you decide by your feelings. Let your intuition guide you.
Don't have a 35mm slide. Well you can make these out of cardboard.