First and foremost, and I cannot stress this enough, get your guitar in the best condition possible. Make sure it is set up properly, is in tune with itself, that it’s tuned correctly and have strings that are very new. Put new strings on several days before recording to give them time to stretch and relax to the instrument.
Check your tuning after every take.
Make sure your amp/cabinet is in good condition. New power tubes, good cords. Extra batteries, if you use them, for your pedals/boxes.
Electric 6 string:
It’s all about the tone. The Shure Sm 57 is still the best all-around mic to use. The newer ribbons are good too. The Sennheiser E609 is another great choice.
Mic the cabinet, try different locations on all the speakers. It’s amazing how different the sound is from speaker to speaker. Plugin simulations are okay but the real thing is always best. Split the guitar signal and record one track straight into the recorder. Try a room mic, sometimes it works sometimes not.
mono: a nice pencil condenser aimed between the sound hole and the fret board is a good starting point. If too brite move towards the body below the sound hole. If the guitar has a bridge pickup use that as well.
Stereo: the xy technique works very well in this situation. Or a mic aimed at the lower body and one aimed at the neck.
If you can, use a DI and mic the cabinet using a large diaphragm condenser or dynamic.
Apply a bit of compression to control level differences between strings.
What are your favorite techniques for recording various guitars?