The body can only build muscle at a limited rate over any given time period, and a huge mistake I made in my earlier years was trying to bulk up too aggressively and too quickly.
I thought that more calories automatically equalled more muscle growth and ended up ballooning to 228 pounds (I'm 174 now), gaining a ton of fat in the process.
A much better approach to muscle building nutrition is a small calorie surplus with a focus on making slow, gradual lean muscle gains. You'll look better, feel better and won't have to go through a drawn out cutting phase later on to lose the excess fat.
Bodybuilding Mistakes: #2 ** Not Treating Joints With Enough Care
When I first started working out I felt invincible and just wanted to make muscle gains at whatever cost. As a result, I ended up pushing the envelope too far in terms of overall training intensity and injured several areas including my lower back, shoulders and elbow that still affect me today.
Things like forced reps, heavy negatives, rest pause etc. are okay from time to time, but they should be used sparingly and aren't necessary in order to get great results anyway.
Bodybuilding Mistakes: #3 ** Too Much Concern For Meal Frequency & Meal Timing
Back when I was starting out, it was "common knowledge" that eating every 2-3 hours was necessary to gain muscle or that you had to consume highly specific foods at different times of day in order to get the best results.
We now know that proper bodybuilding nutrition is mostly just about the big picture and is mainly a product of overall macros/micros for the day as a whole. I wish I knew this back then as it would have hugely simplified my eating plan.
Bodybuilding Mistakes: #4 ** Labelling Foods As "Clean" And "Dirty"
This ties into the last point. I used to sit around eating tuna straight from the can or choking down protein shakes that I didn't want to drink all because I thought that eating certain foods was "mandatory" in order to gain muscle effectively.
Again, it all just comes down to overall nutrition for the day as a whole, and it's perfectly possible to eat foods you truly enjoy as long as they fit into your calories/macros in the big picture.
Bodybuilding Mistakes: #5 ** Over Emphasis On Supplements
In my teen years I went crazy overboard on "muscle building supplements" and took all kinds of different things such as testosterone boosters, nitric oxide pills, amino acid supplements, glutamine etc.
Most of these products were totally useless and I could have saved a ton of money had I known then that the supplement industry is basically just a big marketing machine and that only a select few supplements do anything at all.
Bodybuilding Mistakes: #6 ** Not Enough Scepticism
As a bodybuilding beginner I tended to just accept at face value what other "experts" told me without really questioning it. I didn't realize just how much misinformation there was out there and that much of the advice given is not based on any real hard evidence in the first place.
Had I been more "scientific" with my approach at the start I could have avoided a lot of these mistakes that I've mentioned so far.
Bodybuilding Mistakes: #7 ** Taking Bodybuilding Too Seriously
If I could go back now, I wouldn't have turned down invitations to go out because I was worried about getting all my meals in... I wouldn't have been in the gym training alone on a Saturday night... and I wouldn't have taken the whole thing so seriously in general.
Bodybuilding and fitness is great, and being in shape is great too, but there's no need to revolve your entire life around it.
The truth is that getting an impressive body doesn't require a ton of time and sacrifice to begin with, and I think it's much healthier to have more overall life balance and have fitness enrich your life rather than being the sole focus.