1. First of all, you need to update your Accounting software with GST version for convenient efiling of returns.(Below mentioned points are for Tally)
2. After the update, create these ledgers(create ledgers only which are applicable to your business):
a. Local Sales 0%, 5%, 12%, 18%, 28% each (5 ledgers)
b. Interstate Sales 0%, 5%, 12%, 18%, 28% each(5 ledgers)
c. Local Purchases 0%, 5%, 12%, 18%, 28% each(5 ledgers)
d. Interstate Purchases 0%, 5%, 12%, 18%, 28% each(5 ledgers)
e. Local Purchase from Unregistered Dealers 0%, 5%, 12%, 18%, 28%
f. Interstate Purchases from Unregistered Dealers 0%, 5%, 12%, 18%, 28%
g. Output CGST 2.5%, 6%, 9%, 14%(4 ledgers)
h. Output SGST 2.5%, 6%, 9%, 14%(4 ledgers)
i. Output IGST 5%, 12%, 18%, 14%(4 ledgers)
j. Input CGST 2.5%, 6%, 9%, 14%(4 ledgers)
k. Input SGST 2.5%, 6%, 9%, 14%(4 ledgers)
l. Input IGST 5%, 12%, 18%, 14%(4 ledgers)
3. Ensure that every ledger like Sales, Purchase, Customer, Supplier, Output GST, Input GST, Raw Material, Finished Good etc are configured for GST applicability and enter the relevant details in their configuration.
4. Now when you pass Sales entries, it will automatically go to GSTR-1 format. Same for purchases, they will go to GSTR-2 automatically. Now you can directly file these returns on the portal by exporting this data from Tally.