Data other than pictures ... assuming the files got deleted, you need root access. If the data was in a database file and got marked deleted, you need a SQLite editor, familiarity with SQL ... and root. If the data is in a file that got replaced with a file that has no data, there's nothing to recover.
If the files are on an SD card,
PhotoRec will recover them (you'll need a PC - Linux, Mac, or Windows).