Over the years I have evolved my training methods based upon things I have learned about my body. As I find things that work I try to further refine the techniques to see if I can squeeze even more out of them. I work on things not only with weight training, but cardio as well.
Some things I have taken away from my experiments are that you must change things up regularly and you must push yourself harder than you think you can be pushed. This is a key because most of us don't push ourselves as hard as we can possibly be pushed. You would be surprised how many times you've quit a set before you actually failed. This is just a simple fact. We won't push ourselves as hard as someone else will.
Right now I am focused on some Chad Waterbury principles. I periodize by changing up the repetition scheme on each workout. It keeps my body guessing and so far it is working. As for cardio, I have come up with several ways to change up the intensity. I obviously use HIIT for my mainstay of cardio and just change machines to keep things interesting. However, I also use incline as a means for inducing intensity. I use Tabata sessions to get some fast but intense cardio in. I have also introduced a weekly 5k run into my plan. All of it seems to be working well.
My workout strategy has changed a little in terms of frequency. I am now lifting 4 days a week and doing cardio 4 days a week. The major difference is that I only do 10 minute HIIT cardio on days I lift and I never do cardio on leg day. It really works as well. I have been able to up the intensity of my workouts by handling them like this. It is especially important as we get older to have strategies like this in place.