The most common returns will be GSTR 1, 2 ,3, 4 & 9. All businesses need to submit GSTR 1, GSTR 2 & GSTR every month. GSTR 4 needs to be submitted every quarter and GSTR 9 is to be submitted on an online basis.
Below is a table of all the forms you would need to fill and file under the latest GST regime:

Form Type/Number
What To File
Who Should File
Due Date
GSTR - 1
Outward Sales
By Suppliers
10th of next month
GSTR - 2
Purchases made
By Recipients
15th of next month
GSTR - 3
Monthly return of what went out and what came in (supplies) + payable tax amount
By all businesses
20th of next month
GSTR - 4
Compound GST return
By all businesses
18th of every quarter
GSTR - 5
GST returns
By taxable non-residents
20th of next month
GSTR - 6
GST returns
Input Service Distributor
16th of next month
GSTR - 7
GST returns
TDS deductors
10th of next month
GSTR - 8
Supplies + taxes collected via e-commerce platform
E-commerce operators/ tax collectors
10th of next month
GSTR - 9
Annual GST returns
By all businesses
31st Dec of financial year
 
You can view model forms here. The forms will be available in the GST network (GSTN) and you will need to file them at the portal regularly.