Similar to Litsy’s Roll 100 challenge. You put in the first book of every series you want to read, even if you’ve already read that book, just haven’t finished the series. Virtually roll a set of dice once a month using https://rollthedice.online/en/dice/d100 or another source with a hundred-sided die. Whatever number it lands on is the series you read next. As you finish series, you can add more in to fill the number slots if you have more than 100 series to read, or you can do less.