Okay lets get some clarity: when you see the price of crypto go down don't panic because it is responding to the market (more people buying in, people selling and exchanging for alt coins..etc...) There are only a specific amount of coins that can be sold and as such coins will adjust.
The strategy is that when one of your coins go down, invest a little more money so that when they go up you have more value. Try not to buy when high, unless you are new, if that is that case buy at whatever the price is.
Don't sell bitcoin or litecoin because you see a price dip...this is normal so just hold and wait.
As for your alt coins..meaning coins other than bitcoin, litecoin and ethereum...coins like potcoin, omg, eos are considered alt coins. With alt coins you can watch them...when they dip you can buy more...when they increase you can exchange for bitcoin, or litecoin. I don't deal with ethereum, for my own reasons, but it is one of the top three so if you do, then invest into it.