I started out weight training for sports so a lot of times I was doing basic movements and doing as my coaches instructed me.
After sports ended, I became religious in tracking my workouts. Log books, folders with loose papers, and each loaded with what I did each day. 8 week routines, 12 week routines... I knew each workout I was doing before I got to the gym.
As I progressed more, I learned what worked best for my body. What exercises hit me the hardest and what proved most effective. Also, as I got bigger, it became more obvious what body parts needed to be worked on.
Now, I go to the gym with a goal in mind. I know what needs to be worked on and what I want to accomplish in the gym so I get it done. I don't write things down religiously anymore and my workouts aren't set before I go in. It leaves things open for me to adjust things throughout the workout. If I go in thinking I'll do 4 sets of squats, but after 4 sets, I think I have more in me, I don't just stop! I do another set or 2. If I had a long day and I'm not able to do as much as much then I push myself to the max within what my body will allow on that day and I keep it moving.
I've tried all the training tools and all the methods... from weighted vests, plyometrics, sprints down a football field with a parachute harnessed on my back to basic squats and dealifts... at the end of the day, this is what you need to know:
Set your goals and train accordingly to reach your goals. From there, just remember two basic rules - intensity and consistency... don't overcomplicate things.