Memoirs have a theme -- when you look back upon your life what is one word that describes your life? This is not written in stone. It is a way, at the moment in time you are thinking of one word, that you might think about your life. The word might change in a minute or a day or a week...or...
Write down that word. Did you do it? Great! Next time you get stuck in your writing use that word as your writing prompt.
Your memoir will have people in it - they are major and minor characters. You will describe scenes in your memoir, make a list of your scenes as you go along. Why? It helps you keep track of what you are writing about.
Use short sentences. It provides energy to your work, Pretend you are telling your story to your new best friend - it will help you shorten the length of your descriptions and clarify who you are speaking and writing about. DO NOT USE ADVERBS! In dialogue use "she said," "he said," allow the dialogue to carry the emotion of what is said. USE ACTIVE VERBS. No lazy verbs. Every verb counts and infuses your work with energy.
Put everything in your first draft you want to write. In succeeding drafts lay out your chapters in succession on a table, or on the floor and you will see redundancies in your writing. Maybe you will rearrange your chapters, maybe some characters will be removed or changed.
It does not matter if you succeeded or not in things you tried to do in life - readers will be fascinated by your wins and losses knowing you survived when things were not going well and a reader in a faraway place might be heartened to know you survived to write about your life. The reader may be going through their own trials and you will have given them that precious four letter word: hope.