Few things of many I've learned:
"Biostimulants" - Things like kelp (cytokinin, auxin, gibberellin), amino acids, vitamin B, etc contribute greatly to plant health and growth
Small amount of phosphorus can help promote root development in seedling stage
VPD is important
Learn the PPFD curve and what your plant can theoretically take before needing Co2 supplementation
Record EVERYTHING in some way- be it here, in a notebook, in picture form, however. Just have a record, especially if you're in a legal country with nothing to lose by doing so. Knowledge is power, and much can be gained by reviewing the things you did in previous grows.
Grow with love. The plants will give you back what you put into them in terms of effort.