I used to be a 'fill the frame' guy but lately have started to work with more negative space in the photos.
One of the reasons is that I started doing more street photography and prefer showing people in context with their environment.
I've also been trying some 'rule of thirds'
Rule of Thirds composition as well, it does seem to make photos more appealing.
I hope to take a photo class soon to help me explore this further but for now it is all resources like those mentioned by fuent104 above.
Oh, and of course also trying to emulate the wonderful photos by the masters here has been very educational.