Buy Litecoin and Ethereum at any time and wait until their prices become expensive. These are altcoins, which are ideal for long-term storage. I think that both coins will not fall any more. The dipping of Litecoin and Ethereum has passed, and the rest of January will be very good for these two coins.
I've read lot's of information and it's written that Ethereum is great for short-term storage, cause it's unpredictable