Trading is a good way. Setup an account on an exchange and buy a little of a cryptocurrency you are interested in. Study the charts and try to buy in a dip of a popular coin. Once you bought a coin, set a sell price a bit higher enough to offset your trading fees and to make a small profit. Rinse and repeat until you grow your stack. Just remember to buy low and sell high. 
Yes, trading is the good choice. But what if we don't have a lot funds for buy some coins? And we just know the development of cryptocurrency, what to do?Actually i suggest if we have the funds then trading is the thing to do, but if we don't have a lot of funds i suggest to follow/join a signature campaign or bounty campaign, but you must meet the requirements and follow the rules made by the manager. In addition you can help promote the project about crypourrency, You also get a salary from the activity.