The basic guideline is to be simple and cohesive with the mood of the video. I started out using too many symbols and my comments ended up looking all messy. Now I choose one tiktok emoji to go at the end of a short line that matches the joke/feeling. It's more natural and people respond to me more. Boostbysocial has some great information on what styles work. Try out a few ideas and see which ones are liked.