I'm not particularly fond of gaps in a resume. That's not because they're a bad thing. Life happens, so it's inevitable that gaps can exist in a resume. I'm not fond of gaps because, more often than not, my candidates don't know how to properly explain the gaps. It's a tough conversation to have with people since most of us are self-conscious about professional gaps in their resume.
Most people have a misconception about how others view gaps in a resume. Often times, the general consensus is that it reflects poorly on your application. The reality, however, is that hiring managers - and most competent recruitment consultants - are sympathetic and simply want to understand what happened that lead to your resume gaps. Therefore, as is often the case, honesty seems to be the best policy. With a caveat, of course.
Suppose the last role you had resulted in a firing. Well, this isn't necessarily a detriment to your application. It is imperative, however, that you do not reflect poorly on your prior employer. It's much more important to take note of why you were laid off and, if need be, elaborate on how that incident helped to more deeply 'form' your professional life. Employers are not interested in negativity. Always be positive.
Perhaps it wasn't a layoff; rather, it was your personal decision to leave the employ of XYZ company. Do not insinuate that you hated working for this company. The best way to tell this story, rather than saying how much you hated said the company, is to explain how you learned more about yourself and have consciously decided to seek employment more aligned with your skill set. A practical example is if you're a salesperson who realized they are slightly more introverted than the role requires - thus, you prefer to be more company facing than client facing. Rather than tell the new employer how much you hate sales, explain to the new employer that your objective is to look for employment that allows you to more carefully focus on company-related tasks rather than client facing work.
An important factor, in the midst of explaining your rationale for departing XYZ employer from your past, is to discuss what you have been doing during the gap to better yourself professionally or personally. If you've taken courses or obtained a certificate or consulted (freelance or pro-bono), talk explicitly about it. Emphasize what it has done to help you grow professionally.
The key to discussing gaps in your resume is that you must be honest and positive about your experiences. Gaps exist because either we are particular about the roles we are seeking for ourselves, or because there hasn't been a fit as of yet between your skill set and what the employer is looking for. Always be positive and demonstrate how this new environment is far more conducive to your success as a professional than prior roles.
Gaps are not a big deal in the grand scheme of things. Therefore, it's imperative you relax - and be confident in yourself.