You can easily check the btc price movement and compare it with other top alts, if you view for example the crypto prices in coindesk. You can see the overview of the trend movement, and you will say a lot of these alts are indeed following the movement of bitcoin. But for small cap coins and unfamiliar projects, don't expect that it will follow the btc performance as some of them has their own movement especially if the team is playing the pump and dump game.
From my little experience as a crypto trader most of the top crypto/USDT pair shares almost the same candlestick patterns with BTC/USDT, and possibly similar price movement though most of these Altcoins lag a bit in terms of movement compared to bitcoin, thus I find it easy to do my analysis, whenever I did the an analysis for BTC/USDT it makes it easier for me to pick any other pair with a high volume and market Capitalization for trading thus will produce the same result, moreso once bitcoin is trending positive on the binance App other Altcoins will indicates Positive too vise versa.