These are non-objective and almost completely biased, but they are some ways I have thought of to help a reincarnation story be more realistic and what I feel would be better suited to long term story telling.
No memory from birth (and no 'cultivation in womb' type stuff either, at least consciously). An infant brain is not psychologically developed enough let alone an embryo/fetus.
Regain memories:
•Either slowly/piecemeal starting around age 3 or 4, in which case people/the kid should consider them stories along the lines of imaginary friends. Maybe people think they are a genius, maybe crazy, maybe a freak. The former personality starts emerging bit by bit, random bits of knowledge repeated from memory at times without comprehension or understanding or context. Body dysphoria as memories from previous life jar up against current form/life, feeling as if parents/loved one/life isn't real, nothing makes sense. Then one day, probably sometime in early teens and maybe after some kind of trauma: emotional physical or otherwise, they suddenly 'have all the pieces put together'. Or at least enough for their fragmented and disjointed consciousness to form a whole for once in their life since they started to gain their previous life memories. It won't be the same personality as their previous life, but it won't be the broken and fragmented one either. A new consciousness, and new personality, formed by the combination of their previous life and the torturous perspective of a young teen who spent roughly a decade, their entire childhood, essentially insane and plagued by 'visions', potentially in an environment completely different from their previous life (high fantasy, scifi, cultivation world, post/apocalyptic, etc compared to modern world).
-•-note: in this instance a montage/summarized childhood can be used to time skip through childhood, but flashbacks should be used later in the story to events/people met during the childhood that were not covered during the montage/time skips. A childhood bully may be mentioned, but details about the bully or specific events of bullying they did may be skipped over to become plot elements later on, a parent could leave to be encountered later with a flashback scene of the last time they were seen, etc etc.
•Or regain memories all at once at an older age where the brain is capable of handling them/at least enough of them to be comprehensible. This does have the 'downside' of the new life developing a new perspective and personality without any input from the previous. As such, several additional factors are needed to distinguish this as a reincarnation rather than a transmigration story where the previous mind inherits a new body. These can include, but are not limited to: recurring dreams, unnatural talents/learning speed of physical skills (residual 'muscle memory' leaking through), frequent feelings of Deja Vu (especially if being reincarnated in what was a fictional world for previous life), slips of the tongue/using phrases/slang not native to the world (possibly to comedic effect/running gag), and other sorts of foreshadowing that is often also used in 'memory tampered with' themed stories (looking at you Total Recall franchise). One thing to beware of is not to just erase the 'naturally' developed personality. This is not a transmigration story, so no 'erasing the soul' or 'taking the responsibility for last wish' deals. There can be some struggle/tension when it comes to reconciling with having lived an entirely different life, especially if there are drastically different perspectives and circumstances between the two, but there shouldn't be much if any 'two different people battling/fusing into one to control the body'. Instead treat it literarily (as in literary used as/turned into an adverb, not a typo of literally) as if it is any other major turning point/paradigm shift a character can go through. The 'frog is out of the well', the 'death of a loved one/survivors guilt', the 'had to kill' one, the 'first love and/or betrayal', the 'rite of passage' or 'become an adult' one. In the end an acceptance of who they are/have become, and a sense of gratitude for getting a second (or possibly first/ chance at a) childhood and time to bond with new family/friends without the baggage of past life.
Wishes (if any)
•Should not be remembered (or if they are, not until they are all completed, which can be at the end of the life if they are open ended and/or life long ones like 'to become the strongest')
•should always have at least one mundane one (an no Cooking isn't mundane if it is Food Wars level, especially if it is that level from the start) however this can be 'to have a dream/goal I want to pursue' but only if the first life didn't have one/doesn't have any idea of what to do.
-•- the random 'to have a goal' wish can be a fun way *for the author* to troll the audience by having several things the new life of the MC is talented in/several possible paths or goal they could pursue, but never have them commit to any of them for a while, especially if they haven't gained memories of past life while discovering these talents and etc.
•Should be ways to grow, or for certain circumstances or environments to be part of next life: talents in something that still needs to be trained to maximize potential, a loving family, meeting a soulmate (not picking a specific person, but the circumstance of meeting them), not being poor, or conversely not being obscenely (and lonesomely?) rich, and similarly to be more or less intelligent.