Also if you are still single you need to have Certificate of the marital status issued by Registration Office and ministry of Foreign Affairs in india then take it to thailand and issue that by thai embassy and after formal transfer to thai language to show it to Municipality for marriage . By the way your girl friend also need to show marital status certificate too . Also you need 2 person as Witness who knows thai and english language

If you have thai wife already you should apply for Non-immigrant (o) visa in the thai embassy in your country you need to show your marriage certificate and other paper work to the embassy to get this category of visa .

1 - No need a lawyer

2 - Get Non immigrant (o) visa ( 3 months )from out side thailand in any thai embassy

3 - open a bank account in thailand and deposite 800,000 thb for more than 2 months and then get a deposite certificate paper from your bank

4 - Going to nearest immigration office and apply1 year visa ( 1 month + 11 months ) for yourself and your wife