As mentioned above, you’ll probably find the results of double- or triple-tracking a rhythm guitar part are more satisfying (bigger, wider, more harmonically rich) if there are tonal differences between the tracks you lay down. So if you’re not Jerry Cantrell, you don’t have Dave Jerden to help you, and you don’t have a bunch of extra guitars or amps at your disposal, think creatively.
Something I’ve done in the past to get round this problem is to lay down the first track with a relatively hi-fi, unprocessed, full-range amp tone, a ‘bass on five, mid on five, treble on five’ kind of tone. This will probably be the bedrock of the overall sound, but not always. Then, for extra low-end grit or to make the blend more aggressive, try adding a second part using a grimy, dirty-sounding distortion pedal (Pro Co Rat, Big Muff, whatever you’ve got – I use a Boss Hyper Fuzz for that kind of tone, which is a pretty crazy-sounding pedal, especially in ‘Fuzz 1’ mode). Then to get a top end that really cuts, try using a wah pedal in a fixed position, not necessarily depressed all the way, but enough that the sound really starts to spit. You may get better results if this layer is less dirty and saturated than the others. Experiment, have fun with it.
Remember, too, that the sound coming out of the amp is just the starting point, albeit a very important one. If you’re recording with an engineer in studio, then you can rely on someone with good ears and a lot of experience to place the mic and negotiate gain scheduling (whether to tape or DAW). If you’re a home recordist, then it’s down to you to make sure that you’re actually capturing your guitar sound with the microphone. Two things: first, small differences in mic placement make an enormous difference to the sound of your recording. Maybe at first you won’t hear the subtle differences between ‘good’ and ‘great’. You will in time. And secondly, this is difficult to do well – don’t beat yourself up if your early experiments don’t go brilliantly.
Once the three layers are tracked, adjust the balance between them to taste. If you’ve got a second guitar, you could repeat the process. Make sure the performances are tight and check your tuning and intonation thoroughly as you go. The more precise you are in tuning and performance, the better the result will be.
Pedals. Go crazy with them.