As defined benefit plans continue to disappear, more American workers are relying on defined contribution plans, like 401(k)s, to save for retirement. And because the defined contribution market is booming, many advisors and benefits brokers who've never worked with retirement plans would like to break into this market. They just don't know where to start.

"It is a complicated world," says Phil Chisholm, vice president of defined contribution product management for Fidelity. "It's difficult for an advisor to step in and say, 'Today I'm going to be a 401(k) advisor.'"

That's why he advocates that anyone interested in working with 401(k)s start by aligning themselves with someone who's already successful in that environment. If the advisor's an expert on investments, she could team up with someone who complements her skills, like someone who specializes in plan design or education.