What should I do to maintain GST, if I don't maintain any type of account for my business (i.e. grocery, fruits & vegetable in one shop)?

Every person who is registered under GST has to file GST return quarterly or monthly as applicable. If you are not maintaining accounts, then for filing GST returns you can maintain only data of his sales and purchase with required detail such as invoice no., client name, GST number , Tax paid or collected etc. for taking credit and for payment of tax to government.