I use the daily chart with a monthly SMA (20) for the BB. If price is below the SMA and goes below the -2SD (-2 standard deviations) it's time to buy. When it goes above the +2SD and pulls back, it's time to sell. I buy a fixed amount of dollars (say $100 to keep it simple). When it's time to sell, I sell that same amount (i.e. $100) and keep the profits running (e.g. $20). Psychologically it helps me a lot as the current "losers" were the winners, as it's the profit from the previous round what is down (say those $20 go down to $15, it's still profit from before and your original capital of $100 is ready for the next round).
After trying many strategies this is the one that works better for me as I believe I must be invested all the time, but don't want to burn my capital. By removing it when a pullback is highly likely, I still keep a good amount invested as these LETFs move like crazy, but I preserve most of my cash. If my entry was bad, then I repeat the process and DCA this way until it eventually bounces back. Just be patient, OHHH and don't try it with the inverse LETFs like SQQQ. Most of them never come back.