PREPARATION: GUITAR / BASS:
Heavier strings & lighter picks! One thing that I run into again & again are players using thick yellow picks on 9's or 10's while playing & gripping the guitar way too hard. You pretty much don't stand a chance of getting in-tune tracks with this approach. So with the exception of solo-only guitars, I strongly encourage using 11's on all standard tuned guitars & 12's or larger on guitars in drop tunings. Some brands strings come with both wound & un-wound G strings which is nice but try them both out before the sessions to see which one is best for you. As for picks, certainly choose something no thicker than those yellow Dunlops. I personally use the orange Dunlops which is like a step down from the yellow guys & I feel like those are good compromise.
Get setup! Please have your instrument(s) "setup" & checked out by a professional technician. It costs about $40 per guitar & it will be worth every single penny. A poorly intonated instrument is nearly impossible to make sound good, yes, even through the BEST amp. Be sure to inform them of your normal tuning & what gauge & brand strings you use.
New strings! Please have fresh strings on your instrument before arriving at the studio.
Good cables! Please have high quality cables including patch cables. It DOES make a difference.
Extra batteries! Bring a few extra 9volt batteries.
Please try to write parts that are within your ability to play them. Performing cleanly & consistantly is the hallmark of great musicianship & will always sound & feel better than a million overdubs, edits & studio trickery.
Rehearse! Please practice all your parts, ideas, solos, etc before you get to the studio. It's always the little thing you think won't be a problem that becomes a huge problem. Practice until you bleed! (not really).