Schengen visa for Sweden

Can anyone who has applied for a Schengen tourist visa to Sweden from UAE guide me? I have some questions regarding the application.

1. Is passport a deciding factor in rejection? I am an Indian passport holder with not much travel history. What are my chances?

2. My primary intention is to attend my fiance's graduation in Sweden. Should I have an invitation from him or can I apply as a tourist? What would increase my chances of getting approved?

3. Is there any advantage to applying through external agencies?