In order to choose a coin, you need to analyze the graph of its price. And if the coin is now on the bottom, you can buy it. This will give you a profit in a short time.
Sometimes I'm doing exactly that, and it did give me a good result, but only for short time investment, we'll need a different strategy for long term investment...
Reading whitepaper, and analyzing if the project will bring a huge benefit to the society might be what you need to do for a lont term investment strategy, but sometmes it's tricky tough~