>>51786635It happens to me sometimes. About once a month give or take, though sometimes I don't get any dreams like that for long periods of time.
Thinking about what you want to dream about is important, but what I've found is that overall mindset and emotional state also matter a lot. If I'm in a bad place mentally I might still dream about something/someone I love, but it won't be a good dream. Those are always the worst.