I hate the sound of an out of tune guitar, but so many people have them because they don’t know how to tune a guitar.  The easiest and most accurate way to tune a guitar is to buy a tuner.  It will tell you if you’re sharp or flat, and then you can tune accordingly.  Another way, is by tuning the guitar to itself, but that requires a really good ear, and you can’t be tone deaf.  Keep in mind that cheap acoustic guitars, especially the older ones will go out of tune faster, so you might have to tune more often.