The formula depends on the niche, but some general rules would apply...
In the beginning, start with a focus on quality links. Especially for local sites, getting a listing in that city's chamber of commerce website or city's .gov page is a plus.
If you client retails for larger brands, make sure his/her suppliers link to your client's site when possible.
Press releases can help build brand and authority. Good links on news sites, including some majors, will help in developing an authoritative backlink profile.
There are many other things you can do, and I'm sure others could add to this list. Keep in mind this is not about quantity and about quality. Especially for new sites, it is important to develop a trustworthy backlink profile before going BH on the site. Others may disagree, but for a client that is the process I would recommend.