I am 29, unmarried, having 6+ Years of experience as a Software Engineer in India. How can I get a job in NZ before I apply for visa under 'Skilled Migrant' category?
Many jobs in New Zealand are offered on one of the big job sites, such as http://www.seek.co.nz/ or http://www.trademe.co.nz/jobs. As a software engineer, there are also NZ jobs listed on https://careers.stackoverflow.com/ (those all seem to be Auckland-based when I checked while writing this answer). You can also contact recruiting agencies and companies individually (look for "jobs", "careers", or "vacancies" on their web site).
You may find that many jobs offered say something like "Applicant must have the right to work in New Zealand", which means you need a work visa first. What you can do is try to apply for a skilled migrant visa without the benefit of having a job offer. If you have enough points, this is possible. You can then come to New Zealand on a visitor visa, look for a job (this is a lot easier when you can do in-person interviews), then when you get a job offer you can get a temporary work visa. Having a job will then make your skilled migrant visa process much more quickly.
There are other possible ways to arrange this too. If you have a university degree and 6 years experience, you're definitely on the right track. When I did this many years ago, I found the staff at Immigration very helpful in explaining what I needed to do.