It really depends. The main point here is that you should play around with the variables. If you sell something for younger folk, your best bet is to advertise on TikTok, Instagram, etc.; if it’s for older people, try Facebook, YouTube, Google, etc. If you want to target more specific demographics, you have to experiment with different platforms and methods. Once you settle on a platform(s) to advertise on, then focus on the minuscule details. Look at advertisements that people like and think about what makes the audience enjoy them. It will take time. This is how people become “effective”. A good start is to look at where other people in the industry advertise. They usually have tested multiple platforms and have settled on theirs for a reason.