How do you retain memories from your previous life? The most obvious way is to make sure you have those memories front loaded with as much trauma as you can give yourself. But that's crude. Inhumane. Painful. And above all, unreliable.
You've got to think about the shape of memories.
Shapes is the key, in fact. Human memory is built above all to retain stories by relating them to physical spaces. Places, and their form, and how they attach to each other.
I've confirmed this with some experimental testing of my own. And more - I'm able to create future memories for myself. Mark the thing you want to remember, imagine it in the context in the future where you're going to need it, and it'll be there waiting for you. Easier than writing shopping lists.
Maybe this is obscure advice to anybody else. I don't really know how to phrase it. But picture it: If you assume you're going to die, you make a memory. Just in case reincarnation is real. You try to make a useful memory that your future self can recollect, with no knowledge of who you are. Nothing super intense that will get confused by a baby in the horror of birth, and in the six months before its brain develops past the point of an advanced Alzheimer's patient. But a clear, simple, focused memory that will linger in a child between about age five to fifteen, when it will be old enough to begin checking on things for itself. Maybe something as simple as an email login. Any memory will work, as long as you can figure out the mechanics of recovering that memory without any context. You've only got to plan ahead.
I expect a fair share of today's 1% will try to pass on their memories of Panama bank accounts directly to their future selves rather than their children, just to make generational wealth even worse than Tracy Chapman could have imagined.. Just in case there is such a thing as reincarnation, we should try to work on that.