Whether you have $20 or $200,000 to invest, the objective is the same: to make your money grow. The means, however, vary dramatically based on the amount of money being invested, the state of the market, and your own investing style.
Pay off high interest debt. If you have a loan or credit card debt with a high interest rate (over 10%) there's no point in investing your hard-earned cash. Whatever interest you earn through investing (usually less than 10%) won't make much of a difference because you'll be spending a greater amount paying interest on your debt. For example, let's say Sam has saved $4,000 for investing, but he also has $4,000 in credit card debt at a 14% interest rate. He could invest the $4,000 and if he gets a 12% ROI (return on investment--and this is being very optimistic) in a year he'll have made $480 in interest. But the credit card company will have charged him $560 in interest. He's $80 in the hole, and he still has that $4,000 principal to pay off. Why bother? Pay off the high interest debt first so that you can actually keep any money you make by investing. Otherwise, the only investors making money are the ones who loaned it to you at a high interest rate.