Volatility of the market is the biggest risk. However, how you can turn it into an advantage. Also, be aware of the scams in the market. If you are holding for long-term, store your cryptocurrencies in a cold wallet.
One of the biggest risks of trading cryptocurrencies is to start your journey by trading altcoins, it is my opinion that newbies must begin their careers by trading bitcoin and to forget about altcoins until they have more experience on what to look for in the altcoin market, however newbies get excited about the profits they can get in the altcoin market and instead decide to start trading completely unknown coins, which eventually leads them to a bunch of shitcoins and then they get scammed, losing a great deal of money while investing in those coins.