Currently I own a lot of altcoin, I bought them at ico. My account is being downgraded several times. There are many people who say bitcoin will continue to decrease, so altcoin prices also decreased compared to USDT. So now, should I sell them and wait for the price to buy back? Give me advice 
I can suggest such a strategy. Select the most promising altcoins and hold them. The rest of the coins are exchanged for the Etherium and participate in the new ICO, because now there are good projects