First you need to have some background first in trading. I can recommend babypips because in here you will learn trading step by step because it is like a school where you are in a certain grade and then graduating after you are finished with the level. It is focus in forex trading but in can be applied to cryptocurreny trading as well. You will learn fundamental, technical analysis and market psychology.
After graduating, you may proceed to actual trading. Choose an exchange and trade whatever coin you like may it be against BTC/USD or Altcoin/BTC. I recommend Bittrex because there are plenty of coins to choose from. Only trade what you can afford to lose and never let your emotions do the trade for you but it is easier said than done. Nevertheless, if you lose, just learn from it and move on. It is in losing that you will truly learn how to become a consistent profitable trader.