It's hard to predict which out of thousands of alts will go up, but what you can predict is that once a coin went up, it's bound to go down.
(....)
This will also depend on the pair you are looking for, there are pair that is extremely bullish not the same with Doge which is totally risky as of the moment.
For an example of Ethereum, when it first touched $3,000 before, it wasn't able to see or touched the $2,000 level. And now it is trading nearly $4,000. It's really strong, a lot of buyers, and no one wants to sell. So shorting this kind of alts right now is like doing suicide.
Shorting requires perfect timing and trading skills. Shorting a highly volatile crypto market that is bullish is a recipe for financial disaster. Taking profits on big price spikes is ok though.
There are a lot of instances of why you will short particular crypto. Most of them are surely based on technical analysis.