When I started I got myself a small notebook. Small enough to fit my pocket. I wrote down everything. Any random thought. You know how you'll try something and then wonder why? Well I wrote it down. On the back of every print I wrote down the filters and exposure. Between everything I ended up with a personal info pack. I could look at a range of prints and see what sort of change I'd get from making different changes. Plus I could go back over things outside of the darkroom.