Dear Rachna,
First you have to decide which venture you would like to start. Following factors can be considered:-
1) Interest and entraprenual skills.
2) Expertise
3) SWOT analysis of the venture
4) How much investement you have
5) Target market
6) Competition.
7) etc etc.
You can further search the material on Blue Ocean and Red Ocean Strategy.
Regards,
Vinod Bidwaik