My first paycheck was $1,847 net. I had no idea what to do with it. Here's what I know now that I wish someone had told me then.

The three most important things to do in the first month of your first real job:

1. Sign up for the 401k and contribute at least enough to get the full employer match. Every dollar of match is an immediate 50-100% return. If you don't do this in the first 30 days, you lose those months of matching permanently.

2. Open a Roth IRA at Fidelity or Vanguard. Invest it in a total market index fund. Set up a recurring monthly transfer of whatever you can manage — even $50.

3. Open a high-yield savings account (not at a big bank). Move $500 to it as the start of your emergency fund.

Those three actions, done in the first month, set up the financial infrastructure that runs for the rest of your career. Everything else is optimization.