If you receive restricted stock subject to vesting (every founder does), file an 83(b) election with the IRS within 30 days.
Why: without it, you owe income tax as the stock vests at its (rising) fair market value — which can mean huge tax bills with no liquidity. With it, you pay tax once at formation when shares are nearly worthless.
Miss the 30-day deadline = no fix. Set the alarm.
Next action
Turn the lesson into work.
Pick one concrete next step now, while the context is still fresh.