Sacrifice anything outside of basic living expenses to max out your 401k(or similar), and put more in a non-tax advantaged brokerage if you can. Do not touch your 401k before retirement for any reason. Never take out a home equity loan, do a cash out refi, or roll other debt into your mortgage. (Matters of literal life or death excluded, of course.)

Retiring at 48 with a paid off house beats the hell out of succumbing to the temptation of lifestyle boat in your 20s.