Mark, who handles SEO and communications for a construction firm sent me a note asking about how to set up a link exchange. The answer, like most good SEO advice, is pretty simple:
The big challenge is not quantity but quality. Inbound links from high traffic/high relevance sites mean a lot more than links from sites that don’t get much traffic or are off-topic relative to your site. I’ve had a single good link double my traffic while several less authoritative links did nothing.
You also have to have something to offer to get reciprocal links from good sites- either traffic, good information or mutual benefit such as business referrals (i.e. if you use the same HVAC firm all the time, ask for a link).
Joining associations and business networks can help you get links also but Google will penalize you if the only thing the directory offers are links- they’re wise to that approach to buying links.
Getting links is a sales process- you identify good sources, contact them and offer your value and ask for the sale (a link). If you’re not willing to be proactive about it you won’t get the links.