Make sure your planner fits your lifestyle. Your planner should be organized to best fit how busy your days, weeks, or even months are.
You will spend a considerable amount of time looking at your planner, make it something you will WANT to look at.
Similar to how your planner should fit your personality, it should also fit the vibe you want it to have. If you want something more fun and creative, you should pick a planner with stickers or other cool add ons. If you want something a little more serious, find one that reflects that.
Your Day-to-Day Activities
Your planner should reflect your schedule on a daily basis. If you travel a lot, your planner should be fairly easy to take around with you. If you mostly look at it at your desk, then it could be a little heavier and less portable.
Your Organization Style
If you are a person who likes to have to-do lists, or notes in your planner, find a planner that that has those components.