Now that I am consistent with my lifting routine after years of injuries and being on and off, I have realized that, counterintuitively, the biggest mistake is going too hard at it.
We try to train hard, to the limit and very frequently in hopes that it will make a difference and we will get results faster.
When you stop being in a hurry and realize that lifting is not something you do for next summer, but rather for your entire life, eveything starts working properly.