Hi Anuj,
The most important thing when you justify any switch in a job is not to mention anything wrong about your previous organization as it will leave a bad impact on the interviewer. Secondly, analyze the amount of gap; if it's for a month, it can be well justified by mentioning any personal issue or health issue. However, if it's a 6+ gap, then it's important to analyze the reason why you left the organization - is it the work environment, planning, strategies, and elaborate on the area without being too reluctant in the negative area.
Hope this helps!!
Take care,
Vasudha