Kiklo's answer is the best so far. In addition you need to decide what kind of investor you are.
1. Do you want to buy and hold, trade now and then, or spend all day trading?
2. Do you need to be able to pull your money out fast? If so you should stick to coins that have had a consistent high volume over time. Profit potential is often less in these than other coins unless you plan to be a very active trader.
3. Decide on risk profile. Higher risk mostly has higher potential profit. ICO's are perfect if you love high risk Otherwise stay away. They are often scams, but the successfull ones can be very rewarding. Bitcoin and Litecoin are at the other end of the scale. Relatively low risk, but also less potential for high roi. Personally I prefer undervalued coins in the lower half of top 100
http://coinmarketcap.com/1 They have often been around for a while so it's possible to see if they have a dedicated dev and a good community. You will also be able to see if they have delivered what they promised in the past. These coins can go sideways forever before they either crash or moon, so it's mostly for buy and hold strategies.
No matter what you do, don't trust people that tell you to buy a specific coin. They want you to buy so they can sell!
Do research. Read the ANN's. I tend to buy coins where the team and community discuss development in their thread, and stay away when they mostly discuss price.
Stay away from coins with anonymous devs. (There are a few exceptions to this, but for now stay away)
