I think we have our own best strategy. My strategy is keeping the coins when the market’s price is down or decreasing, and i will sell the coins when the timing is right, when the price going up. So i must keep seeing the market, to see when the time is.
But by doing this you cannot increase your portfolio as there are various strategy which can be implemented I usually prefer to increase my portfolio during dump by buying as much as I can in order to sell it off during pump just like we all do. Sometimes it backfires when emotions takes better control of myself especially during extended bear market situation, it's always better to fill your portfolio by purchasing them or using USDT balance to buy during bear market situation.
Note: This will only work with those who have planned there asset portfolio and have good amount of balance in their Tether wallet to utilise it during bearish market.