TTC but unsure of ovulation

Hello! My husband and I have decided to activally try to concieve our first child over the next year or so. I currently have very irregular periods I will go 2-4 months and have a period every month and then I will go a few months where I only spot. So I am unsure of when I should begin taking ovulation tests my cycle when it's regular is between 35-37 days. Any advise on how I know when my peak times are or when to take ovulation tests?