Install custom firmware such as Unlaunch and TWiLight Menu++
Use a compatible SD card adapter or flashcart for homebrew and backups
Update the system firmware only if required for the mod method you choose
Backup any important save data before making changes
Follow a trusted DSi modding guide step by step
Install Unlaunch through the DSi Camera exploit or another supported exploit
Configure TWiLight Menu++ to launch homebrew, emulators, and DS games
Add homebrew applications to the SD card
Use hiyaCFW if you want NAND-based custom firmware features
Keep a NAND backup in a safe place
Avoid modifying system files unless the guide specifically instructs it
Test each change before adding the next one
Use only files intended for the DSi
Reboot and verify that the modded menu and apps load correctly