How strong does your link building need to be?

With all the different link building methods and other factors like no follow/do follow, PR variance etc. How do you evaluate or plan out from the off, the the diversity and frequency of the types of links you're going to build without doing overkill in terms of time and money spent?

This of course depends on the competition, but with all the different options available, can get a bit confusing as to where to concentrate your resources. Would you start with say article marketing, blog commenting and perhaps a BMR subscription? Then later on down the line, start adding a different set of backlinks if the site is needing a push up the serps.

The reason I ask is if you don't really know what you're doing, then you could easily end up spending more time and money than you really needed. For instance you may end up paying $200 per month for a SEO service but it was not actually crucial in helping your site gain ranking. I guess it would come down to your own experience as you find and get accustomed to what works best for your needs. Is it just a trial and error approach or is there a good methodology to come up with the right backlink plan?

To summarize, what would be the most effective way to go about starting off the link building and what type of links to build?