You would (or maybe you wouldn't) be surprised at how many would-be candidates either have not given this question sufficient thought, especially given the fact that they are making a decision that will impact their lifestyle and career for many years to come. As a would-be lateral candidate, you are asking other people, other professionals, to buy into you, to invest time, effort, and in the law firm world a whole lot of money, into you. On top of the credentials and experience a firm needs to service its client base and expand its future business opportunities (and too many candidates make the mistake of not understanding that firms are absolutely a business first and foremost), you need a compelling story.
When I was interviewing for law firm jobs, I found myself across the desk from the chair of the litigation group at the head office of the firm I would eventually join (and which is now the largest firm in the world). Yes, he looked at my resume and saw my law school, my journal membership, my appellate clinic experience, and everything else on the single page intended to provide the best possible window into my background. But what the interview and conversation really focused on was my perspective on what it meant to be a litigator.
It has been nearly a decade since that day, so this is not a direct quote, but what I simply told the partner was that, when boiled down to its essential elements, the heart of being a litigator is simply telling a story. Your client has a story. The other side has a story. And your job is to take everything you can within the case, the facts, the law, the psychology of the judge (and jury, if applicable), and to tell a convincing story about why a decision for your client is the correct outcome. Much to my delight, since I was trying to convince this partner to hire me, he sat back in his chair, smiled, and said "that's exactly how I look at litigating too." Yes, there is a lot more that goes into it in terms of technical details, discovery practices, evidence, the applicable law, but at the end of the day, as a litigator you are telling the best story you can.
Circling back to your own career as a would-be lateral candidate, you need to be able to tell your own story convincingly enough that the people in charge at a firm, and preferably your top choice of firm, want to bring you on board. Let me rephrase that - you do not just need to tell your own story convincingly, but you need to have a convincing story to begin with. And that can take a lot more thought and a lot more work than most attorney candidates might imagine, or would like to invest in their own search.
So why are you looking to change jobs?
If it's because you are looking to move to a different part of the country, why are you wanting to move there? Unless you have close family there, or your fiancée or spouse already moved out ahead of you, there needs to be a compelling reason behind your decision. You are trying to convince a firm to invest in you and your career, both in terms of the opportunity cost of choosing you above all other potential candidates, but also in terms of moving expenses, salary, training, support staff, and the time and energy it will take the partners and other associates to bring you into their matters and get you up to speed. If you've only visited an area a couple of times, and just happened to "like" it, that is not very convincing, especially to firms in smaller cities and legal markets. They want to hear that you know a lot about the region, that your desire to be there in the long term is greater than your desire to be somewhere else, and that you will stick around. So give it as much thought as required so that a solid answer will roll off your tongue when the question inevitably comes up in an interview.
If you are looking to change jobs because you are unhappy at your current firm, you will need a compelling story about why you are unhappy (i.e., you are being pigeonholed into a practice area you do not like, and NOT that the hours are too long or you have difficulty getting along with the partners). If your story is that you are tired of working big firm hours, or that you've been at the firm for a couple months but it isn't working out because of hours, a clash of personalities, or because the work is not what you expected, you are basically telling a story that you are not a dedicated, hard-working attorney, did not do your due diligence in researching your current firm, and are not a team player. Your ideal story is that you are on an upward trajectory at your smaller firm, and want bigger and more sophisticated opportunities at a larger firm. Or, alternately, you have been very successful at your larger firm and have a number of prospective clients, and the only thing getting in the way of developing your own significant book of business is the prohibitively high billing rates at your current large firm, which is why you are seeking to join a sophisticated mid-sized or boutique firm.
If you are looking to change jobs because you want a higher salary (an extremely common reason among job seekers I talk to who are in solo or small practices), it is fine for you to want to make more money, but you will have to tell your story in a compelling manner to a firm as to why you are worth more than you currently make and will provide more value to the firm than any competing candidate for their open position. If you are struggling to attract and retain clients at your current firm or solo practice, what are you bringing to the table to your would-be future firm in exchange for a higher regular salary? Perhaps some of your clients have legal matters that require a larger and more sophisticated set of services than you or your current firm can provide, and thus by joining a larger firm you can expand both your own business and bring in additional business to that future firm. But if that is the case, you need to be able to tell that story in your business plan and interview responses in a detailed and compelling manner.
As a legal recruiter, it is my job to inform a firm why the candidate I am representing to them is the best candidate for their open position, and will bring significant value to the firm's practice expertise and, above all, their bottom line. Similarly, our client firms ask us to convince top candidates that their firm is the best home for that candidate and their book of business - still telling a story, just with the roles flipped. At the end of the day, attorneys have all sorts of reasons why they are seeking to switch jobs, but you will not have a successful search unless you first get your story straight.