As a doctor who has lifted weight for the past 12 years, is now hitting towards that 'middle age' area of life, and have taken personal study to athlete's and lifters lifestyles and lifting habits, there are a few things I have taken with me. I am 6'2'' and 190 pounds. I am not a huge guy. I am not the strongest man. But I am consistent and realistic. And I have had to research and overcome quite a few of my own sports and athletic injuries and have helped numerous patients do so as well.
In no particular order:
1. Be consistent, the turtle wins the race. Especially for you young guys and girls out there. If you are 20 realize that you have hopefully another 50 years to train, and about 20 years to train and feel good and make progress, assuming you are natural, which most people are. Don't hit it hard for 3 months and then barely train for the next 2 months. Be realistic. I feel I can train safely and have a balance in my life if I train 3 days a week. I could probably do 4, but I like 3. If I have to, I will do 2 days, and one day at home I will train with body weight and dumbels or bands. Key is, train year round. Except:
2. Except: take training breaks. Long term damage to tendons and tissue, through training, especially as you get older, or acquire more injuries, require you to take breaks. This doesn't mean sitting on you ass. It means instead of lifting 4 days a week, walk on a treadmill for 40 minutes two days a week and do yoga once. Stretch for 20 minutes a day for 7 days. Use a lacrosse ball and foam roller to work the beef jerky out the best you can. AND REFEED.
3. Eat well, and eat enough. I can't stress this point enough. This may be #1 even though I don't have them ranked. Know where you are on your weight and strength, know where you want to be, and eat healthy, dense meals. Do NOT be afraid of healthy carb foods. They will make you grow. Eat a lot on both training days and on non training days. Meal prep. Stay away from junk. Eat enough vegetables and fruits. Eat enough fermented foods. Drink enough water. Take supplements like BCAA's, creatine, B-complex, D, and magnesium.
4. Perform weekly mobility work. Do not train yourself into a cage of strength and no athleticism. As you age, you WILL get stiffer and have a decreased range of motion. This is natural. Get mobilizing and get stretching, and get comfy with the amazing discomfort doing this brings.
5. Try different approaches to your fitness. Some may seem to work better for you. 5x5 or higher volume total body, cardio on same day versus other day, dumbel vs barbel work, different angle, cables, unilateral work. And also learn to try different things if you find yourself with injuries or discomfort.
6. Train postural muscles and little muscles. The weak links. Rotator cuff work, lateral knee movements, internal/external leg work, hamstring work, mid trap work, and of course, glute work.
7. Don't work through new pain. You will regret it, I promise. That's a surgical referral or at the very least months off of training recipe. Elbow pain? Rest it. Start slow, doing eccentric work. Do tissue work on it and mobility. Long term joint problems of the tendonous type require a walking of a line approach. Degraded tendons need direct work, blood flow, and tissue work to stimulate remodeling, but one should know where the line is of further injury. Long term tenon injuries will break the rule of 'no pain no gain', but it should be slight and should not 'flare up' for weeks after rehab. Tissue work, direct tendon stimulation via a work load, rest, sleep, and TIME will remedy the situation. My patellar tendons became painful for an entire year after two years of training mixed with too many weekends of large alpine hiking, with no enough rest. It took 6 months of decline board eccentric squats with both legs planted, to then start slow mild weight leg press, to then start LIGHT barbell squats. I still am making progress, and it's been frustrating to no end.
I've dealt with the same thing with my elbows. An elbow brace worn during work, eccentric wrist curls (pronated), finger bands for extensor work, and Chiropractic and ART done on the lateral epicondyle and just distal fixed them. I still am working on strengthening my elbows and still wear an elbow brace (essentially take load off the extensor tendons) on heavier push/pull days. Lastly, GRIP strength will be of major help in not developing elbow issues in the first place, as will not doing the biggest range of motion of every exercise. It's ok to perform 75% ROM.
8. Sleep. This is all I need to say. SLEEP.
9. Stay out of relations with friends, significant others, family, work that you feel like you are made less of or suppressed by. I've seen so many people start to get injured when they feel suppressed or feel like they don't get to keep their integrity or choice due to someone else. I know this is simply my opinion but we know that the mind has a major effect on physiology. Be in environments which you find to be positive and where you flourish and prosper.
10. Don't let your ego disarm that thing in your head that says this last rep or this much weight is a good idea. Know when to walk away.
11. Get help with your body. See a PT, Chiropractor (find one that takes radiographs and is a modern doctor, all elite athletes have one for a reason), I've seen naturopaths help people quite a bit. Massage therapists of the deep tissue kind are also very helpful. I've seen sauna's help people too if used properly.
12. Drugs and alcohol are not good for the body. I don't care what anyone says, most of the medical community, certainly all my colleagues across medicine, therapists, chiropractors, PT's, surgeons, all agree. This includes many Rx drugs. I can get down with things like CBD, but not THC, etc. Don't discredit my entire post because you may disagree with this point.
13. If you are not an athlete competing anymore, don't train like you are. Be happy you are exercising and stay injury free.
I probably have many other suggestions but I saw this thread and thought I would add to it.