Assuming you want to invest in equities (which can be a whole other discussion), the biggest mistake newbs make is waiting too long. Don't try to devote months to learning things, because even after doing that you won't know anything. Just sign up for an account somewhere (it's relatively painless) and start putting money into the appropriate Vanguard target retirement fund. You can always change your mind and reallocate later, but you can't go back and pick up on lost gains that you missed out on because you were too scared/intimidated/clueless to open a brokerage account. I have late-20s coworkers who have all substantially all of their assets in high-yield savings accounts (or worse) and it pains me to hear them say that, but hey, it's their money.
