Generally when a hero, villain or anything superhero related gets announced is when you want to sell a comic as that is when the hype is at its peak usually for a couple months after the announcement as well. Then the time to buy a comic is after the movie, tv show, or streaming series is out as hype will have gone down as a lot of people will still buy when they first learn about something to make sure they have it. It can be a waiting game. This is just a general rule of thumb to go by. Trends are now dictated by popularity due to exposure of a character. This can also lead to speculation if you can accurately guess the direction something is headed.