don't store them by day or month by any means. you should have a datetime or timestamp field with your data. you would use your query to arrange data by day, month, time of day etc.
without knowing what you want to store it is hard to say. You should know your data. Do a quick read on DATABASE NORMALIZATION so that you have an understanding of this basic concept.
then design your table(s) without data and post them here. People will have an idea of how to help you adjust your table.