There are usually a LOT of differing opinions on how to set the mixture screws, but this is how I was taught:
For the following adjustments go 1/4 turn at a time giving the engine about 15 seconds between each adjustment to react to the new setting.
I usually start out at a baseline from the following: Slowly and gently screw the mixture screw in until you feel it bottom out. Do not force it, as you might damage the needle or seat. Once it has bottomed, turn it back out 1-1/2 turns as the base to start at. Do this for all four mixture screws before proceeding below.
Start the engine and run for 15 minutes or so to warm it up.
From that baseline above, start screwing one screw out (richer) 1/4 turn at a time til the engine starts to stumble from being too rich. Then, counting the number of turns you make, screw the screw back in 1/4 turn at a time (leaner) until the engine speeds up slightly or dies from being too lean. Stop there and remember how many 1/4 turns you just made. Now screw the screw back out half the number of 1/4 turns you just screwed it in. For example if you screwed it in 8, 1/4 turns you would screw it back out 4, 1/4 turns. It should be very close to being right. Repeat this for all four mixture screws and you should be done.
I usually (at least on my own car) note how many 1/4 turns I ended up at, out from a too-lean position and what that was versus bottomed out and write it down somewhere in my tool bag. Then, if I want to make it slightly leaner or richer I can turn it in/out 1/4 turn at a time and still make them all match, OR return them all to where I started later on. I don't get into altitude changes enough to warrant changing jets so the above will suffice.
Just remember to be patient - you're looking for very subtle changes in how the engine is running at idle so, don't rush it - watch (and listen) carefully.