One of the things that really hurts a recording is an out of tune instrument. It can be the take of your life, but if it's not in tune with the rest of the instruments, it's gonna sound like garbage (not the band).

Use a tuner. Don't trust your ears. I usually tune up before every single take. I know this can get a bit time consuming and repetitive, but it's worth it.  

I often use a twelve string, so I can vouch for the repetitive argument. I have a tuner on each of my effects boxes, plus I have a stand alone chromatic tuner. It doesn't matter what you use, just make sure you use a tuner before each and every take.

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