If you're a diploma in mechanical engineering, a broad range of opportunities are in your way:

1) You can go for higher studies abroad, how to do it is summarized by QadSquad in this link below

http://qadsquad.com/higher-studies/higher-studies.html

2)  Get a job in core sector, apply for jobs in. Government PSUs like HAL, DRDO, ISRO, ADA, ADE, GAIL, SAIL etc., after the Make in India initiative by government lot of new jobs are being advertised by these PSUs

3) Get an internship, if you're finding difficult to get a job without experience

4) Register yourself on job portals of different companies like GE, 

Siemens, Honeywell, Bosch, Airbus, Boeing, TVS, Tata motors etc.

Last but not least, keep reading the books, they are your ultimate friends, 

Hope this helps

All the Best !!!