i've seen more shooting stars at random than when isabelle mentions them at the beginning of my log on. if it'll help, try looking up on youtube what the shooting stars look and sound like - they make a very specific sound that you can hear that will alert you to pan your camera up to the sky to wish on them. it wasn't until i had heard it a few times while seeing the shooting stars that i clued in that the sound was related ^^
also, if you're trying to make a wish on a star and your camera is already set, make sure you aren't carrying anything that can be used, like a shovel or a fishing rod. when you press 'A', instead of trying to make a wish, you'll just end up activating the item in your hands instead and could miss your opportunity.
i hope this helps. when i first started i had absolutely no idea what to look for or expect. c: