The key to changing careers successfully is to be absolutely clear about your career choices and career options so that you can implement a targeted job search strategy.
Choosing a new career direction, or job opportunity, is essentially a research, planning and decision making project. You'll carry out the following three steps:

Your career choices will be greatly informed by what you have done in the past. Considering changing careers for example? It's important that you understand what have you've liked in the past, what didn't you like, and why.
Also it means thinking about what your past needs, values and motives were, and deciding if these are still relevant today.
In terms of your career choices, how well can you concisely describe or summarise:
Does all this seem a little overwhelming to you? Well, one way of overcoming this is to take a step by step approach, which is what career planning is all about.
Why you are considering leaving? Are you doing this for the right reasons?
There's also the complete opposite career research question for some people is to examine - why aren't you leaving your present job or career?
This page - changing careers - look before you leap - has a number of questions to help you to fully explore your motives for either changing careers or not making the change.
Another extremely important step in determining where you are now in life and career is to undertake a thorough career review. The questions you'll explore in this process will provide extremely valuable insights about your past that will help with future career decision making.
A relationship breakdown is a common reason for people to examine where they are in their career. Divorce for example often requires people to re-think their career priorities and choices - but this need not be a self sabotaging step. It is also advisable that you seek out any other support you require to deal with your divorce.

If you are a man in midlife and mid career another potential key trigger for career change is midlife crisis.......and yes, this is quite real, and quite serious for many men.
In addition to carefully thinking through your career options, I would recommend that you inform yourself about what midlife crisis is, and seek suggestions for managing this if this is happening to you.
Once you've completed your career and life review you can begin to research your career options and make informed decisions about your future.
What you'll do next is:
All of these actions are related to the career planning process. Using this process makes decision making about your future a whole lot easier.