What do I put in a new brokerage account, if 6 years away from retirement?

I'll be getting a monthly social security check that I want to save in a brokerage account. I'd like something very safe, and to save on taxes if it makes sense? I would greatly appreciate any advise. (maybe in the future I'd invest in equities, but I'm covered as much as I feel comfortable with now in IRAS, etc)