You can read hundreds of books on style. So if you are interested in improving your memoir through the way you tell your story, I encourage you to read a few books on style in writing. What I want to talk about here are some basic things that you should always keep in mind, whether you are writing for your family or for a wider readership.
First, be consistent. Don’t say 11 in one part of your manuscript and e l e v e n in another, unless you have a good reason for it, such as a street address in which you must use numerals. Don’t spell out a state name after using the name of a city in one part of your manuscript and abbreviate it in another part. Don’t spell it council in one part and counsel in another when referring to the same word with the same meaning. Hire an editor if you have to, but fix these errors, which can put off any reader fairly easily and mark you as a real amateur.
Second, think consciously about how you are addressing the reader. In the previous sentence I am writing directly to you, using an imperative sentence structure. You probably won’t be doing much of that in your memoir. Most memoirs are written in the first person (I remember) but some are written, at least partially, in the third person (he remembers). Whatever you choose, be aware that you are indeed choosing and that there are other choices. Same with tense. If you want to use the present tense, do so, but do it sparingly. Do not, please, write your entire memoir in the present tense unless you want to tire your reader quickly.
And last, think about the concept of time in your memoir. You don’t have to tell things in the order in which you experienced them if to remember something that happened later in time before something that happened earlier will make for greater dramatic effect. Experiment with what works best for your particular piece and your particular audience.