Have you read 81 Little Lions: An Introduction to the 9x9 Board for Advanced Beginners, by Immanuel deVillers — Revised Edition (2019) (i feel like its time to bump it on top again ^^) EDIT: hah @yebellz beat me to it >_>
I havent seen much strategy recourses on 9x9, but basically what you want to do is:
- as white (playing with 5.5 komi) to make 2 independently living groups, OR split the board into 2 ~equally sized halves / territories.
- as black, to stop white living with 2 separate groups or make sure that your half of the board is significally larger than whites part of the board.
White will usually win by making 2 living groups, cause those with komi is usually enough to make sure that black cant find enough points to win.
Note that on 9x9 the direction of game will be decided really early, so thats why most 9x9 resourses are about opening, because after 8-12 moves the game is mostly just about middle game fighting and outcomes rely on players reading skills.