Depends how aggressive you want to be with it but I would spilt it up into 5 bits then pick 2 coins from the top 25, another 2 from the top 25-200, and then one coin outside that for a pure gamble. That way you diversify and at the same time are in some solid coins too.
50 dollars is nothing for the market of the cryptocurrency. however, even here, you can make a very small profit (as the start). You can try to buy very good but cheap altcoins like TRON, KickCoin, and Gladius.