How to deal with losses?

Firstly, accept it. If it goes down it goes, there nothing you can do. Don't be held up by how many % loss, believe in it.
Secondly, hold it there don't panic sell or buy. Most of the time for me I'll just ignore that stock, it helps.
Lastly, ask yourself if it worth it to sell/buy now? Read comments, article, news (take it with a pinch of salt)
However the most important lesson is do not believe in what other people say about any specific stock, do your own research and only invest if you believe in that stock