What’s a good time to start a sticker chart for positive reinforcement?

Man my 18 month old is little miss independent! She throws tantrums if she doesn’t get what she wants and is just a whiny butt sometimes. I believe she’s going through her 18 month regression, but I want to start enforcing a sticker chart for positive reinforcement. When would be a good time to start that? And what sort of tasks/rewards would you recommend for a toddler? I understand it may be a bit early, but I would like to get it started!