Presumably, because I've been in a position to be on the receiving end of the pitch process. Well buckle up, we're going on a short ride!
#1 - Check their website to make sure they accept submissions. Some will open submissions from time to time, so you may have to wait a bit.
Don't inundate that editor with e-mails, messages or phone calls. Try to remember these people tend to be very busy. They may not respond because they have to prioritize their workload and communications.
When sending pitch packages, always acknowledge that you realize they are busy and try to remember to thank them for their time looking over your pitch. It certainly can't hurt to let them know you understand how busy some of them can be.