Make sure you have enough emergency funds before investing. More than a few times, I've had to liquidate an asset to pay for some emergency only to watch the stock grow immensely right after selling. Make sure whatever money you invest won't need to be touched for a long time.
Emergency fund is important, but don't go overboard. Remember the average return on a savings account is .01% annually at most banks, versus an average of 7+% in a well diversified portfolio long term.
Also one thing I want to reiterate, a wise investor once told me: Returns aren't guaranteed, fees are.
To put this in perspective lets assume you put 100K in investments and just let it sit (no further contributions, etc) and averaged a 7% return. At the end of 25 years you would have roughly $542K. If you paid 1.5% in advisory/brokerage fees annually that would be reduced to $381K at the end of the 25 years. (And if you're really curious if you put that 100K in savings at .01% instead you would have roughly 100K still).