Since more and more people have basic recording setups at home, it's very likely that any player on almost any level will be asked to record some guitars for someone at some point. When it's pro we call it session work, but regardless of what level it's at here is some good advice.
Recording is a challenge because it exposes all strengths and weaknesses in your playing. For that reason recording can be a brutal experience, but when you play something you're proud of you get to keep it forever! So it can be a very rewarding experience and it really hones your chops.
Write out a chart!
... doesn't matter how simple. Just the chords or the form- anything to look at while you play. It really helps you relax, even if you know the song!
Keep it simple!
Recording really makes you aware of how little you often need to play! So don't be scared of playing something super simple. Open chords as whole notes, strumming, single notes etc.
Get your headphone mix right
I'll talk more about this later, but the more professional the situation is the less I try to talk. But the one thing that I make sure to get right, even if I have to adjust multiple times is my headphone mix. It will make all the difference in how comfortable you feel. Is one particular instrument too loud?! Can you hear yourself enough? Or too much so it's freaking you out? Or do you need some reverb on your guitar to get inspired. Get it right!!
The cool thing about recording is that you can just delete whatever you don't like and keep the good stuff. Therefore you can really take some chances and be bold! If it's bad they'll just delete it
You can layer as many guitar parts as you want, so don't think you have to do it all in one part. Lay down a take of whole notes, one of arpeggiating chords, etc.
Just Play the Chords!
This piece of advice I actually got from drummer Kenny Aronoff, and it applies to pros as well as hobby players. If you've grown up playing in bands you're used to playing "parts" and when you learn a new song you'll be searching for "the part". This is ultimately cooler than just playing chords, but it takes much longer to find a part and often times people don't even need it. They just need the chords, the sound of your instrument, a certain feel, etc. This had made a huge difference in the quality of my session work!
Bring a sweater and a snack!
This might be self explanatory in other parts of the world, but in L.A. you often just leave the house in a T-shirt, and then you get to the airconditioned studio. Sometimes they'll have you set up in front of the vent, and you never wanna be the guy with a million requests. It's much easier to just bring a shirt!
- Also... Bring some energy bars! Studio sessions often start at noon and you often go until at least 7pm, before anyone even thinks about eating. And being hungry is terrible for your concentration!!
My friend Reggie said it the best: The only way you're gonna seem like an amateur is by talking too much! Don't analyze everything out loud, just listen and play! Obviously this is different with your friends, but this makes such a huge difference in your appearance to other artists/musicians/producers/engineers.
Obviously you can also do so much in your practicing to help prepare you for recording. Even if you don't have a recording setup you can practice as much as possible with a metronome. 10-20 bucks or you can find a free one online. Even if you don't play with a click when recording it will help your groove/rhythm/timing and make you sound so much better recorded!
Also, make sure your instruments' intonation is adjusted. Otherwise you'll tune yourself to madness and never get it right
Other than that the best advice I ever got was from GT's own Mike Olekshy who always told me "JUST GO HAVE FUN MAN!". I would always think it didn't apply to whatever audition, tryout or exam I was nervous about, but in reality there's no musical situation that doesn't get better from you having fun. You can be hard on yourself at home, but once you're on the gig you JUST HAVE FUN!
Hope this helps. Please post any comments/questions in my forum so we can be sure I see them
All the best,