How should I invest $20,000?

If I woke up in your shoes and found $20,000, here's what I would do:

1) pay off the credit cards, student loans, and/or car note. (Preventing a debt from growing has the same impact to your net worth as making a gain in the stock market, but it's a no-risk move).

2) set up an emergency fund.

Cash in the bank, just in case I lost my job and it took six months to recover.

3) if 1 & 2 were already done, I would invest.

The best investment style is often the most boring. Parking it in an index fund and letting it sit for 40 years is a perfectly workable strategy.

The question is so vague that it's meaningless. You start by considering your specific financial situation and objectives.

idk. Where are you in life, what do you already have, and what do you want?