I found that as soon as I started keeping a training journal, i could monitor when I grew the best, strength gains, fat loss etc.
It also motivates me to train when I am taking strain on the diet and i struggle getting up a flight of stairs.
It's an A4 288pg book.
On the first 2 pages I glued clear folders under the heading Goals and diet.
In there I put the goals and the current diet I am trying to acheive.
I then work out my training regemin for the following few months, and inbetween, I put pics of bodybuilders and motivational quotes.
I write everything I eat, hours I slept, my heart rate in the morning, reps, sets, notes on form and feeling of muscles during training, BF%, weight etc
When I look back, I can see when I grew the best and lost fat the best, how over trained I am, if I can go more, which program worked best etc.
It's been an invaluable tool in my growth