Explain honestly why you have had any employment gaps and make the most of what you have been doing during that time such as volunteering, caring for a relative, studying etc etc. You could prepare to return by looking at the skills required for your new job and getting yourself up to speed - for instance I have just been successful in getting a new job, but for me it is a career change. One of the skills needed in the job description was advanced Excel usage; I had used Excel quite. bit but in a basic capacity so, prior to the interview, I completed an online course to refresh and update my Excel skills. It's hard to suggest specifics when we don't know what it is you are applying for. Best of luck!
In starting back to work after 6 years. I just put on my application that I was caring for my 4 children (1 is very disabled) I drew on those experiences in my personal statement where I thought they might be relevant to a new job. I said I had good organisational skills (trying to fit in various hospital appts and admissions for my son around caring for my other children. I attended various meetings where I sometimes has to think on my feet and be pretty resourceful to get the right support/equipment for him from professionals with limited budgets) There are so many life experiences relevant to lots of jobs, and if course your previous employment. Good luck