Make it non-linear
Classical predictable revenge story goes usually around this timeline:
- Villain cause Tragedy to Victim (Hero)
- Hero cannot defeat Villain just now, so he need to
- get gear
- get training
- get friends
- get weapons
- get informations
- Hero try get his Revenge (and maybe fail, so back to previous point)
- Hero wins
Each single point can be repeated as many times as needed, in no particular order, creating its own sub-quest. When all subquests and main quest are finished, the story ends.
So to make it less predicable, you can just change the order of Chapters.
Start with the Hero somehow equipped and trained and put on classical heroic story (barbar Conan cames to mind) where the Hero arrives to some Place, solves some Quest, win some Treasure, loose big part of it and departs to other Place.
Repeat few times, while you introduce Hero and the World as side-effect.
The Hero did not forgot the Tragedy, but does not talk about it to strangers, when not needed. So we can see him arriving, shopping etc. then he just "talks to the right (shady) people and get interesting hint about <this subquest entry point> so the next day he goes there" (and we do not need to hear all the talks, so we - as well as those shady people - suppose, that the Hint was just for getting Treasure. Hero is good known to readers now as for some "marks" like some scars, big sword etc.
Next Chapter could be simmilar, (just the Hint is something else, maybe local Beauty kidnaped by bandits) and you insert some "real hint" like when describing the Beauty you say, that she looked like Marianne, so she catched Hero's eye (and do not explain Marianne now) and Hero goes to save her. Award may be bigger sword or more scars.
Next Chapter can be about a Boy (without scars and sword) trying to survive in winter and get off hungry wolves.
Next Chapter introduce Hero with more scars and bigger sword and awards him some special/characteristic fighting skill.
Next Chapter is about Girl overcomming some problems. On the end somebody calls her Marianne.
Then Chapter about the Boy in summer, with some small equipment in hills, where he fight with Orcs and get scar (oh, so it was our hero after all)
Next Hero gets some company (and more scars).
Next some Other Person fights some problem and get Position.
Next Hero gets some Contacts as result of <this Chapter subquest>.
Next Chapter the Other Person (younger version) does something terrible to some Villagers.
Next Chapter Hero finally confronts The Villain (which may look like just next Sub-Quest). Hero wins and tells to the dying Villain, that Marianne was Heroes sister and one of those Villagers, that Other Person decimated 20 years ago.
And so it is all clear now and the book may end.
Adult Hero known and described by other name (Lonely Lion) than the Boy (Johny) and their connection and the nickname is explained relatively late.
Villain causes Tragedy also near the end of book and it is not clear, that it is The Tragedy, as Hero does not talk about it too much (it still hurts).
Chapters are not dated, so the years are not obvious and could be decided only in retrospection. (But there should be some hints to connect them in right order later - like characteristic scars, some friend calling Lone Lion as Johny and so - usually introduced much later, than the <Chapters Main Character> is introduced)
The book starts like other genre and Revenge motive sneaks inside much later (or even at the end).
I described it as Fantasy (which is easy), but it can be in any setting and it would just use other "marks" say car, clothes, typical way of speach or words, ...
I would also introduce more side-characters, with their Chapters of history and let them go to other Chapters as friends/enemies/changing sites/double-crossing/villains bodyguards/etc/etc and connect them fully only in few last Chapters to make the World much richer and complicated. And the Revenge should sneak inside by small steps, which are more clear in retrospective (like Heros dislike for some types of characters/situations, occasional curse, little strange/unexpected behavior ...)
My point is, that even totally predicable timeline may be simply obscured and presented as much wider story, than it looks to its autor.