Now I know there are thousands of variables involved as well as opinionated ways of doing this, that's why I'm going to tell you 5 tips I use to make my guitars stand out to help make my mixes sound huge!
1. Double Track Your Rhythm Guitars:
You can easily thicken up the sound of your mixes by doubling your guitar tracks. Yes I know this is not really a 'mixing' tip but when you use both guitars in the mix it can beef up your guitar tracks. PRO TIP: You can even play around with changing the tone slightly on the second track to add even more emphases on certain characteristics of the playing. Say you want one to be more beefy and use another for note clarity. Just one of many ways you can use that to your benefit.
2. Pan Those Tracks:
The next step is to pan those rhythm guitars you tracked. I like to start at hard panning them both, one left one right. If they are sounding too separate bring them more to the middle, 70-80 is a good area where I like to put my guitars, especially for the slower parts. Faster more intricate playing can benefit from going all the way left or right. Panning these guitars helps separate the sound and clear up the middle for other instruments (i.e. kick drum, bass guitar) that need to be there. Turn that pan knob and immediately hear the results.
3. High Pass Filter Your Guitars:
OK yes, I know this is situational depending on the tone/style of guitar you are tracking. But in most times I mix I like to roll off some of those lows to clear up the bottom section and help your guitars not 'fight' so much with the bass and kick drum. I like to start in the 100,200k area and roll it off accordingly to the mix. Let your ears do the work, roll it off as you listen to a section and when you hear the guitars start to'thin out' back off a hair and Voila! You now have cutting clear guitar.
4. Did Someone say Plug-ins?
Yes you read that correctly. But dude, I thought you are always preaching 'crap in crap out, get it right from the source and you wont have to fix anything come mix time??!' Yes you are correct. I do live by that, but remember music and mixing is an art form. There are rules, but there are not. Weird right? I like to look at using plug-in's like using salt when cooking. You don't want to add too much because it will taste bad, but using just enough will make whatever your eating taste much better! Don't be afraid to add a little compression, or tube saturation/distortion to give your tracks get a little more omph! Experiment, you might find something you really like!
5. EQ Subtraction
The last tip here is my all time favorite, and yes it does play off of tip number 3. Subtracting EQ in certain bands is an ideal way to let other instruments in your mix cut through in return making everything (including your guitar tracks) sound bigger, cleaner and overall better. Especially with high gain guitar tracks cutting some of the lower (or) higher mids out is a good way to tone it down and get your guitars working in cohesion with other primary instruments. Don't be afraid to get the scalpel out and start cutting EQ like your a mad surgeon. Just remember to do it while you are listening to your mix, never solo your guitars and start cutting that would not be pretty.