I'm on a tier 2 general visa in the UK. I'm currently engaged and soon after my wedding, I'm planning to bring my wife along with me to the UK to stay with me for 3 weeks. She will then return to India and complete her internship and education. As we are not married yet, we do not have a marriage certificate and we will not be able to obtain one before she files for her tourist visa. Can you please suggest the list of documents which will be required to successfully obtain her tourist visa ? Since she is a student, she is dependent on her parents for her finances. Is it okay to write a cover letter/invitation letter from me stating that we are not applying for Tier 2 dependent visa as she has to go back to India to complete her education and will be away from the UK for around 180 days to ensure that her visitor Visa is approved ?
The UK publishes a guide to supporting documents for a visitor visa here https://www.gov.uk/government/publications/visitor-visa-guide-to-supporting-documents/guide-to-supporting-documents-visiting-the-uk
There is nothing you personally can do to ‘ensure’ that her visitor visa application is approved. It may help you to read How to prove that you have significant ties with family in your home country? and What details should a good cover letter contain to back up a UK Visit Visa application?