The market seems to go through cycles on what is hot. But most of the time, there are trendy industries. Some I understand, many I don't. I usually steer clear of industries I don't understand. And the ones I do understand a bit, I've learned not to try and time the bottoms or tops. As the profits mount, I try to pull some off the table as I go along (I lost a lot of money in the old days trying to time the top, and left holding the bag).
There are many excellent traders/investors on this board.
Good luck to you,
yield