That amazing phenomenon where you don't know shit about training and nutrition but you build muscle and strength anyway. It's a magical time. Everything seems to work because you've gone from doing nothing to doing something. And something always beats nothing (unless congress is involved).
But newbie gains don't last and progress slows. Now you have to start using your brain and filling your toolbox with effective strategies. Here's some general advice.
Build Your Training Toolbox
This is mostly about mindset. Example:
"For legs, you ONLY need to squat with a bar on your back!"
I may have said that myself 20 years ago. Today I realize that there are many ways to hit those muscles and that movement pattern – dozens of different squat variations that work great and allow me to "work around" beat-up knees and various old injuries. Luckily, I'd filled my exercise toolbox with squat alternatives and variations.
A bar on your back is a great tool. Adding more weight is a great tool. But if those are your only tools, you'll have a tougher time progressing when you hit a roadblock. I know, lots of tough guys will disagree. And many of them will also be getting hip replacements by age 50.
Don't be the guy who uses the word "only" a lot when it comes to training topics. His toolbox is sparse and his go-to tools will get rusty.
Get Better Nutrition Tools
The same thing goes for nutrition. There's a common misfire in the young lifter's brain: he thinks he can always eat the same way and get optimal results. In reality, he may be just "getting away with it" temporarily. As your body ages and your life changes, so should your diet. At 45 you're not eating for a 25 year-old's physiology anymore. There's a word for guys who try to do that: chubby.
Maybe it's stress, maybe it's all those extra responsibilities interfering with your workouts, or maybe it's just a body that's getting older and slowly accumulating minor problems. Don't visualize 25 year-old you when you plan your nutrition. Your life is a bit different now. That usually means you're going to have to tighten things up, diet-wise.
Expand Your Supplement Toolbox
Maybe you didn't need that "edge" before, but you sure do now. And a funny thing happens after the age of 40 or so: You start to think about the length and quality of your life, not just about how big or strong you are.
Maybe all you cared about before was a "pre-workout" to frazzle your brain for leg day. Now you're thinking about not contracting some preventable disease by age 55. If I had to choose only a few supplements for long-term health, I'd go for Indigo-3G®, Flameout®, and Superfood. Those go into my nutrition toolbox first.
Fill your toolbox with different training and diet strategies. When your favorite tool doesn't work anymore (or the damn thing goes missing), you'll have plenty of other options. Under 40? Ditch the dogma and start filling that toolbox now. T Nation is your free hardware store.