Like Jei-Cos said, find poses that the character you are cosplaying does frequently (like a battle pose for instance) and try to copy it. If they don't really have an identifiable pose, think of a few that fit the character's personality. You can even google things like "cute poses" or "tough guy poses" or something, if you're really stumped. You can also try looking at fan art and see if you can draw inspiration from there.
I always find three or four different poses for each character and I practice them over and over in front of a mirror, until I am able to position myself perfectly without having to look at myself. The biggest trick is knowing your angles, and which angles work best in front of the camera. You almost always want to have your eyes visible to the camera, so even if you are doing a pose where you are looking off to the side, cheat your head so you can still see your pupils. Nothing looks weirder than only seeing the whites of your eyes lol Another tip- don't squish your arm into your body. If you're doing a pose where your arms are down, or crossed, or otherwise would be pressed against your side/torso, pull your arms away from your body a bit, otherwise you get unintentional arm fat.
But yeah. Definitely pay attention to tutorials, they will have all sorts of tips like this.