The safest and most conservative way would probably be investing in top 10 coins. These would be the main coins you can find on Coinbase. (Bitcoin, Ethereum, Litecoin, etc.)
However, if you’re looking for high potential growth you will want to look into Alt-Coins with lower market caps.
Diversify your portfolio and hold onto the assets for 5+ years and see how much profit you have accumulated. This is not a get rich quick scheme, you will need to do some planning as well as holding. You CAN get rich quick, but you can get even more rich if you hold for the long run.
Selling is not safe in the current market unless you’ve already been holding for a couple years.
You can learn more about investing in Cryptos here.