Make a game out of it for your viewers. The entire purpose of the thumbs up is to reflect engagement... so be engaging! Don't just tell your audience to 'like this video...' they are sooo sick of hearing that. Tell them that if they don't give this video a thumbs up then in the next video you are not sharing your cookies. It doesn't have to make sense, it just has to be fun. Give your viewers a reason to give you a thumbs up and they will... the same goes for getting them to subscribe, to share your video, buy merch etc.