To be effective at acquiring links, it pretty much comes down to the fact that you need to provide something on your site (some content, some tool, some resource, etc.) that cannot be easily found on thousands of other sites on the web.
If you have low quality or mediocre content/tools/resources on your site then you're likely going to be stuck with settling for low quality back links. No webmaster (especially an authoritative, reputable site) is going to "want" to create a "natural" or "editorial" link to some site with crappy content. Sites like these tend to only have the option of building links through "unnatural" methods where you "plant" a link to your site on someone else's site such as article submissions, directory submission, blog commenting, forum sigs, etc. Beware the Penguin.
So your "strategy" should begin with trying to answer questions like...
What does my site offer that would greatly benefit my visitors as well as visitors to other related sites in my niche or complementary to my niche? What great content do I have? What great tool(s)? What great resources?
I can't emphasize GREAT enough... in the above questions.
If you already have a great piece of content/tool/resource then try to think of what other types sites on the web have visitors that might benefit from that resource.
For example, if you have a nursing resource site then there are literally thousands of nursing associations that (while maybe not high in PR) are VERY relevant to your site that are often willing to place a link on their site to yours for their members to access as a resource. Nursing departments at community colleges might have a resources page where they would place a link to your site. These links will be as valuable if not more valuable as a source of referral traffic than the are a benefit to your site's SEO.
If you don't have anthing worthy of attracting quality back links then you need to turn your focus to what you "could" build that would be worthy of quality backlinks and where those desire target link placements might be. Start thinking of things like...
What great content, tool(s), or resource(s) can I develop that has not already been built 1000 times that will be VERY useful and/or informative to my target audience, that will save them time or money, etc?
And at the same time be thinking of...
What quality, relevant, authoritative sites exist that are frequented by my target audience and which would find my content/tool/resource useful for their visitors as well?
Then of course you need to build such content/tool/resource.
Once you have the content/tool/resource (either old or newly built), take time researching placements where you'd like to get links... Forget PageRank. Look for sites that are closely related to yours... sites where YOUR visitors (or the visitors you want to attract) likely hang out. Visit those sites, get familiar with them, determine EXACTLY where on those sites you'd like a link. Build a spreadsheet of the name of the site ("Joe's Plumbing"), the URL where you'd like placement, find contact email (phone number and/or email address), hopefully a real person's name at each site, etc. Find out if they are on Twitter, Facebook, and/or LinkedIn and connect with them.
Then come up with a plan to contact them (either by phone or email... please no FORM emails. Each should be catered to that specific site).
Once you've done all of this then you can spend your $100/month having someone make the calls or customize emails for each site and send them out. If you actually have a great piece of content/tool/resouce then lots of times you need only make the other site aware it exists.
It's not easy, but it works... Getting quality links starts with having something of quality (great content/tools/resources) for other webmaster to "want" to link to.
Read through MartiniBuster's old posts here. Lots of great ideas. Also Eric Ward is a great resource.