A valid passport with at least 6 months validity from the date of arrival.
Two passport size photos. One will go on the form, second is a backup. Photo should have white background witth 80% face visible. Your teeth should not be visible in the photo, so no smiles.
One page visa on arrival form. Carry the filled form from home itself. It will help reduce the time you spent at the visa queue.
Attach return air ticket photocopy with it.
Also, attach hotel booking voucher. Hotel booking should have your name on it. Try to have all names of people on the hotel booking form.
You have to pay 2000 Baht (Rs.4000) as Visa Fee (Per Person). This fee can only be given in Thai Baht.
You should also have 10,000 Baht (Rs.20,000/-), this is proof of adequate finance for your stay in Thailand. In case of a family, you should have THB20,000 (Rs.40,000/-)
You will get immigration card in the flight. If you do not get one, you will get it near the immigration counter.
Give this with your passport and rest of the visa documents. They will staple this with your passport where they stamp your visa. You are required to show this when your return from Bangkok.
If you lose this card, you have to fill a new one and you will be waiting for half to one hour with the imigration officers.