When you start a new project or a new job, it helps to have a set of tools available that you can depend on. For me the most important tool is the notebook I keep about ongoing projects. This is where I write down new ideas, stuff I tried, approaches that failed, and successful solutions.

Keeping a laboratory notebook is standard procedure in every lab where stuff is invented and eventually has to be patented. To chemists, biochemists and phycicists the lab notebook is the most precious document in their labs, because it documents their procedures. It allows you to backtrack and to repeat a procedure. It catches and documents your errors.

As Howard M. Kanare writes in his book Writing the Laboratory Notebook:

Few, if any, working scientists writes notes as carefully and completely as they should. Often a seemingly unimportant detail turns out to be crucial. Much experimental work could be better understood, and much repetition of work avoided, if only researchers were more attentive in their notekeeping. The effectiveness of a working scientist can be increased by considering the important role that a notebook can play in experimental planning, observation, and analysis of data. [...] Finally, but perhaps most important, students who are beginning scientific research must be taught how to create a proper record of their work.