One of the main things that helped me with passing an OSCP exam that I kept to this day was to keep solid notes from any engagement I had a pleasure to participate.
Why would you not treasure the information that you have spent days, sometimes weeks chasing just to let it flee once the problem was solved. It is sure as sugar that you are going to face similar situation in the future and refering to your notes will allow you to solve the problem much quicker and move on to new challanges. That is how you grow.
Besides the experience you write down, the process of penetration testing becomes much more managable and fluid as one phase informs another and gives you a direction of where to go next. Not to mention that when a report writing time comes your findings will be much easier to put together for a client to see.