I previously offered 3 tips about writing a good memoir and you can find that post here.
One thing that seems to help sales of memoirs is targeting a much smaller audience. Somehow, when it comes to writing a memoir, that seems like a crass statement - "targeting an audience." I didn't, or at least I didn't know I was, when I wrote, MY SECRET MOTHER, and I'm guessing that if you are writing your memoir, you aren't either. However, if you plan to publish, it helps to know that there are people who are benefiting from, or at least enjoying your efforts. For most of us, writing a memoir (or anything else) and hoping the entire world will read it, is nonsense - they won't. In most of our cases, 99.9% of the world don't even know we exist, let alone care to read about our lives. So, how much is .1% of the population - you figure it out. (hint: in the U.S. alone, that's over 350,000)
I have mentioned in other places that I continue to be surprised by the sales of MY SECRET MOTHER and that, other than the links on my blog pages, I don't do any actual marketing for it. Here's what I think has happened. I am an adoptee and have spent much of my life wondering about what that meant and how I should act, react and proceed, based on this fact. I wrote about my own feelings and thoughts around adoption, and I addressed the whole thing to the mother that I have never met. I don't think that many writers are writing specifically to birth mothers from the post WWII era, although there is lots of info out there about adoption in a general sense. Sounds like a very small market doesn't it? Maybe that accounts for the success, in terms of sales.
A few readers have passed on the title to other people they know who are connected to adoption in one way or another, and it gets mentioned in relatively (in a marketing sense) small groups of women, and so the word spreads among them. A small sliver of the population still represents a lot of people in a numerical sense.
You might consider looking at your memoir in order to find the unique part of your life and experience, and making that your focal point.
If you concentrate on the uniqueness and use even a small amount of SEO to create your title, or sub-title, and use similar search engine optimized phrases in explaining what your book is about (what your book is about - subject of a blog in the near future), then you should expect to make some reasonable inroads into that marketplace. If my personal experience is any indicator, it would appear to work.
You might want to look for the life experiences that may not be shared by many, or the little-known hobbies and interests you enjoy, maybe the small corner of the world that you grew up in, something that sets you apart, but not alone, from the teeming masses. It will give your memoir a unique flavor and ring a bell with a group of readers that share a curiosity about that slice of your life - and perhaps theirs.