A few books have been written about this subject, most notably Change Your Career: Transitioning to the Nonprofit Sector by Laura Gassner-Otting and The Idealist Guide to Nonprofit Jobs for Sector Switchers by Steven Joiner. (My book, Jobs That Matter: Find a Stable, Fulfilling Career in Public Service, touches on this as well).
The main point to remember when transitioning between the private and nonprofit sector is that you are switching cultures (I was an anthropology major, and it comes in handy sometimes!). There are different values and mores, as well as different terminology, dress codes, and expectations between sectors. The nonprofit sector is all about mission, all about the cause, and often all about heart, with the financial bottom line being important but ideally not the main driver of the work; while the private sector is mainly about the financial bottom line with other priorities being important but not the main driver.
In the private sector, the people you serve are probably called customers, consumers, or clients. They are likely buying something from you. The other organizations that might try to serve these folks are your competitors. Your money comes from serving these people, and selling them a product or service. Your job is to make money for the owners or shareholders. Even in these times of lean management, for-profit companies tend to have the money to buy big computer systems, hire extra support staff, and expenses-paid trips to conferences and events.
In the nonprofit sector, the people or mission you serve can be called many different things—and it can be quite politically charged what to call them, so make sure you know what term each organization uses. Also, the way you are helping them has different names. You have to be aware of the power dynamics involved—most likely, a human services nonprofit is not “helping the poor” or “reaching out to at-risk kids” but rather “empowering low-income individuals” or “reaching out to refugee and immigrant youth.” Your organization might not even be serving people—rather you may be organizing people around a cause, or saving orca whales, or researching the cure for a disease.
The other organizations that might serve the same cause are probably partners and stakeholders, not so much competitors (really, there isn’t supposed to be a lot of overlap in nonprofits all providing the same service to the same group of people). The money comes from charitable donations, foundation or corporate grants, and is not tied directly to your work the same way as it is in the private sector.
Results are measured not in dollars, but in outcomes—which can take years to measure and might be hard to tie directly to the work you are doing. In most nonprofits, there are no extra resources to be used to buy a fancy new office or hire extra support staff, so people must be creative to get the work done.
To make yourself a good candidate for a nonprofit job, you have to consider which skills you have developed which may be relevant to a nonprofit. Some skills and job titles easily and more or less directly transfer, such as human resources, communication, IT, or accounting. Some can translate, like a transition from sales to fundraising, as long as you think through how to present your experience and possibly add some volunteer leadership to your resume to build skills specific to the nonprofit sector. Others take a lot more translation, like managing programs.
Do the research and the networking, and you too can make the leap from the private to nonprofit sector.