Bitcoin up = altcoin down
Bitcoin down = altcion down
Bitcoin stable = altcoin moon
Trading is not that simple and you have to look out for many other affecting factors when trading. This theory might work sometime but it will not work always and you might loss all you have when trying to follow this simple strategy.
You have to only trade coins with high trading volume and never buy when it is pumping hard. At the end traders will look at price in USD of a coin rather than in a BTC so keep that in mind when making your moves.
It's not easy since its so though to think on which one is the best to be traded today and which one is needed to avoid with plus the pressure we can get for trade stats happenings plus another fud handling. And there would not an easy aspect of it since it can rotten our mindset if we are not ready to take the risk beneath on it.