Just do things that increase testosterone and make you more manly. Heavy lifting, eating more salmon and meat, olive oil, not giving a fck, etc. Get good sleep. My beard growth has improved over the past few months due to some of this (besides the good sleep). Then again, I'm 22.5 years old so maybe I'm still maturing.
Externally, I bet you could use things like light dying or daily application of olive oil/product to increase the perceived thickness. Men have been doing this for thousands of years. Luckily (a good beard is pretty awesome) and unluckily (shaving almost every day when I'm in a professional environment is kind of annoying and irritating to the skin), I don't have to do this.