Long-term investments will pay off over several years. You should determine the rate of return you want and look for a mutual fund that averages that rate of return over a five or ten year period. When 
you invest for the long-term you should not panic when stocks drop and you should not sell when the market looks bad. The market has always recovered from drops in the past, although it may take time to do so. However, if you pull out when prices are low, you lose the money that you initially invested. If you leave your investments alone ,then they should recover over time.
The longer you have to invest your money the bigger the risks you can take.
If you need the money in the next few years, you will want to take a more conservative approach to your investments and may opt to put it in the bank or another more secure type of investment. Another factor in choosing the type of investment may be what you are planning on using the money.