For me, my strategy is to sell Bitcoin when it goes up and buy Altcoin instead, and vice versa, i.e. I sell Altcoin and buy Bitcoin when the price of Bitcoin goes down.
Usually, after Bitcoin goes up and starts to go down a little, it is a good opportunity to buy Altcoin, some of which starts to go up at this point, but of course you have to do your own research and know how to choose good Altcoin with a good project and potential for future growth.