I’v used some of Japanese textbooks and actually there are 2 types method to sort Japanese verbs. First one, Group 1 is -iます and Group 2 is -eます。 For example, かきます、よみます are Group 1. たべます、いれます are Group 2. But Some of -iます verbs are Group 2(みます、おきます……) Second one, Group 1 is -u and Group 2 is -ru. For example, かく、よむ are Group 1. たべる、いれる are Group 2. This method also has some of irregular verbs. For example かえる is Group 1. So you can choose which one is easy to remember or understand. I hope it helps you.