I'm 29 years old, originally started training at about 17 years old. I've had years of serious training, years of fuckarounditis, years of complete sedentary due to lumbar disc injury, I've even worked as a personal trainer.
Read and re-read the FAQ, a lot of what I'm saying is already there.
Before I begin with tons of randomness, I want to say that there is no 100% right way to train or to eat, no perfect program or diet, and knowing your own body and its reactions to things like stress, training, rep-range, nutrition, macros, etc, is the only way to maximizing progress. Therefore, I cannot ever begin to suggest what will work for you, only what's worked for me in hopes that you can formulate your own plans using some of these tips. Trial and error is your best friend, don't be afraid to fail - as long as you get up, dust yourself off, and try again.
Training for Hypertrophy, opposed to Strength training
I'm sure the vast majority of people browsing r/fitness are training for vanity - they want to get big and lean. I know strength is a huge theme for r/fitness, too, but overall, people start training to gain muscle, not strength.
I too trained for years for hypertrophy alone, mostly in the 8-12 rep range. While I made much progress, I rarely increased the load, and progress would often halt until I changed up my programming. Broscience often got in the way of doing what really needed to be done, and that's to build a solid foundation of strength before ever trying to train for hypertrophy.
Even though I had what most would consider a very solid foundation already, after my "off" period due to major lumbar injury and surgery, I decided to work on strength over hypertrophy.
Starting Strength is known as a beginner program, but it's for anyone looking to maximize linear progression in terms of strength - something that is very important to anyone interested in getting "big". The results were astounding, and I have progressed more in terms of load numbers on six months than I had in six years of hypertrophy training. As a result, I also put on a great deal of muscle mass, and lost bodyfat. Granted, I was very overweight at the beginning, and much of my gains were through muscle-memory, but I've greatly exceeded where I was prior to my injury (and at that time I was a personal trainer).
Since my linear progress slowed, I decided to switch back to a hypertrophy routine. And while yes, I increase my load less often, I'm getting much better results in growth due to how heavy a load I can handle for higher rep counts. Nearly double where I was when I was training for hypertrophy. Plus, my core is stronger, I'm more resistant to injury, etc. I do still include heavy compound movements in every session - I feel this is a must.
Another important tip: Stick to your program. Results take time. If you're not seeing any results after 3-6 months, then rethink. But you'll never see a major improvement in just weeks.
Diet and Nutrition for Maximizing Gains
Eat. Eat. Eat. And eat some more. There's not much more too it. Any and all "hardgainers" just aren't eating enough. There are fast metabolisms, but you are likely still just not eating enough. If you're lucky enough to have a fast metabolism, you can get away with eating less than "clean" foods and still make progress while staying generally lean. Look for calorie dense foods like whole milk, peanut butter, and beef. Total calories in are more important than calorie timing, but I find that feeding every 2-3 hours is easier to bulk than consuming huge meals that leave you feeling like you ate a few bricks.
Diet and Nutrition for Recomposition and Fat Loss
Most gurus will tell you that recomposition is nearly impossible, or at least extremely difficult, and to instead choose to cut or bulk. If you're heavy, or were heavy, it's scary to eat as much food that is necessary to bulk, so recomp is likely the best way for your comfort zone.
Recomposition is possible, as long as you plan according to your training schedule. Carbs are required to replenish spent glycogen stores in muscles, allowing for proteins to rebuild muscle fibers. As such, eating plenty of carbs on the days you train to refuel your muscles is vital to growth. But on your "off" days, drop carb intake to a moderate level, and increase your healthy fat intake. Things like avacado, salmon, and almonds are excellent sources of healthy fats. Use calorie calculators, and macro-nutrient calculators to find out your maintenance intake, then add 500 calories to your training days, and subtract 500 calories on your off days. Progress will indeed be slower, but it is possible.
For fat loss, as simple as this may sound, but you must lower your calorie intake. How low you reduce your calories below maintenance by (250-500 is recommended) is up to you and how fast you want to lose weight. Total calories consumed is the most important part of any diet, but paying close attention to macros is also important. Lower, to moderate carbs are best for losing fat. And it's a good idea to cycle your total calories consumed and carbohydrates, to prevent homeostasis from occurring.
Whether you are trying to gain mass, recomp, or to lose fat, I cannot stress enough the importance of properly tracking calories. Do it for a few days, and I guarantee you will realize that you are missing your target calories. Even the slightest discrepancy could negate progress, so pay attention, write it down, and adjust accordingly.
Cardio for Fat-loss
Cardio is wonderful for conditioning and overall health, but it can feel like a chore. To maximize your fat loss through cardio, a combination of HIIT cardio and low-intensity cardio is best.
What's always worked best for me is 10-20 minutes of sprints, 30 seconds of all out sprinting followed by 30 seconds of active rest until your time is up. Whatever you can handle at first, slowly building to 20 minutes. Going over 20 minutes isn't recommended as it can eat into your gains or cause muscle loss at a calorie deficit.
Low-intensity cardio, like long medium-power walks, roughly 40-60 minutes twice a week in a fasted state are key. To reduce muscle loss on a calorie deficit, consume some BCAAs before low-intensity cardio in a fasted state.
More Random Tips
Back pain? Always check with a doctor first. If it's a severe injury, rest is the only option, followed by controlled rehabilitation. Don't overlook or train through pain, it will cost you. If the back pain is moderate, you need to reexamine your form, focus more on mobility and flexibility, especially in the posterior chain (hams, glutes, lower back), and strengthen your core. I highly recommend a book/program called Foundation by Eric Goodman and Peter Park. After two herniated disks, lumbar surgery, and years of pain/pain meds, this program got me back into the gym, and I'm deadlifting nearly 400lbs again with no pain.
Can't do a pull-up/chin-up? Don't do assisted movements, and instead opt for negatives instead. You'll soon be able to perform even one full chin/pull up. One turns into two, then three. Keep going until you can reach a full set. Keep mixing in the negatives with full reps until you can perform a full set.
Supplements? Caffeine, Fish Oil, and Creatine. You don't even need protein powder if you're eating enough. Protein powder like Whey or Casein are for convenience and cost. I do recommend them, but they're not the holy grail some people think they are. Other supplements do indeed work, but they're likely not worth their cost. That all comes down to how much you want to spend - but do your research first. Examine.com is an excellent resource. I personally use Scivation Xtend in the AM, along with a pre-workout mix (Jack3d usually), then for post, I consume 8 ounces of grape juice and a scoop or Optimum Nutrition Whey. At nights, to keep calories down, I have a scoop of ON Casein if I don't feel like eating.
Rest! Get 8 or more hours of sleep if possible, or as close as you can. If you can't, try to nap. Make sure you're taking at least one day off a week, preferably more. Remember, growth takes place during rest. Training just provides the stimulus that triggers growth reactions. Those triggers are no good without the building blocks (calories/macros) and rest.
Routine and Dedication. No diet or training program will ever work well if you're half-assing it. I suggest logging every workout, ever meal, ever calorie, etc. Keep to your schedule, stay motivated and dedicated. If you can't, you only have yourself to blame for lack of progress. I understand life gets in the way, as does injury, sickness, etc. These cannot be avoided at times, but as long as you are giving it your all, you cannot be stopped.
Pretty much all of this is common sense, and it's in the FAQ. I've wasted years at a time by listening to broscience or mens fitness magazines. Instead, stick to tried and true methods that come from real life experience, blood, sweat, and tears, and you will go far.
I just came off a five year hiatus due to severe injury, pain, and lack of confidence, strength, and self-worth. One day, something clicked inside me, telling me to not let the pain control me anymore. Now, I've lost 75 lbs while gaining significant amounts of muscle, increasing my strength to advanced levels (for example, I went 135 > 345 sqauts/3x5 in six months). I'm healthy, I'm strong, I'm happy, and I honestly cannot believe it, I'm pain-free. Sure I wake up with stiffness and have worse days than
others, but compared to where I was just a year ago, I am a new man. I owe it to smart programming, strict diet, determination, but most of all, knowing my body, listening to it, and adjusting when necessary. It's something that usually comes after years of experience, but learning to channel it early on can lead to less trial and error, and faster progress.