This is something probably everyone has heard, but I want to stress anyway. Many employers offer participation a 401K or 403B (for tax-exempt organizations) plan. These let you sock away up to $16,500 a year (more if you're over 50) on a pre-tax basis. That's $16,500 invested instead of something like $5500 paid in tax and $11,000 net income (exact amounts can vary widely depending on your tax bracket.)
These are called tax-deferred accounts because eventually, when you withdraw from the account, the withdrawals will be taxed as income. But you're getting decades worth of compound interest in the meantime. In theory. If you can find an investment that's actually turning a profit.
At any rate, if one of these is available to you, and you can afford to do without the money in the moment, this is one of the single best ways to invest, as a substantial amount of what you're investing is money you never would have seen anyway, as it would have gone to taxes.