get familiar with key signatures first, then you will have some idea what chords will most likely be in a song

Iron Maiden will most likely have a lot of stuff in Eminor

also don't let yourself use an electric tuner, find a song that has open notes in it like Black Sabbath 'war pigs' (it has open e in it a lot) or Led Zeppelin 'the song remains the same' (the intro has open d played over and over) and tune your guitar using that song