Buy low price, sell high price, old trading system still work untill now buddy.
Buy low and sell high is a common strategy for most traders.. but this is not enough that you can make a profit.. better to research first about the altcoin so that you know if the altcoin has a long term life and the project is good if not you should find another altcoin that has a potencial to growth and its a long term project.. before you start to buy cheap and sell high..
That's it ,we must check first the market potential of any alt or crypto currency .because there are many coins that goes on the market ,also many of them are just scam coins i think.