I don’t think there is such a thing as a right balance. If you market yourself properly on the web, you’ll end up with a certain number of NoFollow links, for sure, but I don’t think you need to hit a perfect ratio.
That said, NoFollow links probably still add some value. Not in the PageRank sense, but in the general buzz about your brand on the web sense, especially when they appear in contexts that are not likely to be compensated.

Hi Eric, thanks for the reply.
Actually after reading your blog I’m kinda figuring it out which strategy will suit my website i.e. Transtutors.com. As it lands in the category of Educational websites. We tend to help students with their assignments and homework.
Can you suggest me, which path to follow?

We used a mix of informational and commercial queries. These covered many markets, including health, information, and technology, but also more pure informational queries.
As for the type of backlinks, stay away from blog commenting and article submission as a way to get links. With guest posting, you also need to be very careful to not implement a campaign just for SEO purposes. Guest posting can be a part of a larger scale marketing program, including PR, social media, and other forms of promotion. If you think about yourself as implementing a branding campaign online, and you get a lot of links as a result of that, you are more likely headed in the right direction.