While the good old pen and notebook work well for taking field notes there are lots of tricks and technology enhanced ways of taking notes. If you favor a more old fashioned note taking strategy organization can help. Here’s one strategy.
Cornell method… find a full description here, but the idea is simply to divide your notes page into three parts: your notes of what is going on; cues, questions, prompts; and a summary. These three space can be adapted to your own needs, and will need to be for research purposes as this method was developed for taking notes in class.
It looks something like this, in the abstract and and example. You can generate your own template for the Cornell method as well.