I train primarily at home. I have a badass home gym no word of a lie. But when I do train at a commercial gym there is one thing I always notice. I am the only god damn person with a notebook writing down my training information. Why does this bother me? How can you possibly track and record your improvements if you never wrote it down? If I am sweating it out in the gym but not improving than I am wasting my goddamn time.
So what are the important things to record in a training journal? Well, I have some opinions. I think that volume, density and load are useful training parameters. Suppose we deadlift 200lbs in a 5 X 5 configuration. A 200lb load on a deadlift with 5 sets and 5 reps per set is 5000lbs of volume. Then I record the time it takes me to deadlift my 200lbs for 5 sets at 5 reps per set. Suppose it takes me 10 minutes, this is the density or the amount of work done in how much time. Now next time I dead lift 200lbs I can look at my previous time and if I did not improve my volume or load than perhaps I lifted the same amount of weight in less time.
Some people who keep detailed training journals can actually look back and see that they tend to lift heavy and break load personal records on periods of the month. That is a little out there but it may be worth a try and if not a training journal will still benefit you immensely.