You need the following:
1. Copy of your I-20
2. Copy of your passport / visa
3. Copy of your I-94
4. Your transcript
5. If you want to support financially (for their travel expense, room and board) then fill out I-134 form.
6. Your bank statement
7. Copy of your apartment lease (if you say that they are staying with you) (I think this is optional, but I did it)
8. A letter to your parents inviting them (This is just a formality)
9.  A cover letter to the consular to grant your parents visitor visa.

These are the documents that I sent.
Your dad needs to show strong ties to Nepal such as:
1. bank balance
2. Property
3. Letter from his job (if employed) or letter showing he is receiving pension (if applicable).

Hope that helps

Cheers