Many players on the unending quest for guitar tone often overlook key elements of the sound in favor of some new gadget. There are quite a few simple, and often inexpensive, ways to improve your sound.
Picks come in all shapes and sizes. Experiment to find the best for you in terms of feel, thickness, and precision.
There are as many styles and varieties of strings as there are players. Wound, unwound, different composite metals, gauges, and on. Experiment! Beware that changing string gauge affects other aspects of the guitar, like tension on the neck, intonation, and more. It can become even more complicated if you use a floating tremolo like a Floyd Rose.
Set It Up
A proper setup is absolutely critical. Your instrument can be set up in a variety of ways. Neck relief, action, intonation, pickup tuning, and proper contact points are just some of the factors in a thorough setup. Some players favor a lot of relief, some guys like to shred with really low action. Some players prefer the sound of the pickups close to the strings with polepieces flat, other prefer to move the pickups farther from the strings and crank the polepieces up higher. In the end, it's all about what gets your sound where you want it to be.
If you play really loud or with a lot of gain, overwound pickups can do you more harm than good. Many of the greatest guitar sounds of all time came from weaker pickups through a cranked up amplifier.
Guts and Glory
It takes a little more electronics knowledge, but get in to the electronics cavity of your guitar and look around. Your electronics could probably use an upgrade, especially if you have a lower-end model. Often times the electronics is skimped in favor of cutting manufacturing cost, so replacing the wire, capacitors, and potentiometers can often yield a better response from the instrument. You can also have fun with different pickup wiring configurations and the versatility they can provide.
Swapping speakers is a great way to improve the response of your amp or cabinet and get different tones.
Don't Plug In
Try playing without plugging in from time to time. It can reveal sloppy playing when not hidden behind a bunch of gain. On the other hand, if you often play without plugging in, practice some more plugged in. The feel and response of the guitar definitely changes when an amp is involved, but the bottom line is: practice how you are going to perform!
Sometimes all you need is a fresh perspective. Consider transposing licks played on the bass strings to a treble string variation, or the other way around. Moving licks to different registers is a great way to come up with alternate arrangements or new riffs entirely.
Guitar Strap Height
Yes, the guitar-around-the-knees gunslinger look still drives rock n' roll (at least the photoshoots!), but play with the guitar where it feels right to you. Don't sacrifice sounding good for looking cool.
Quality of cable, as well as total run length can have a huge effect on your sound. Running a large amount of stompboxes can add to tone degradation. Use a high-quality, low-capacitance (which most are) cable like Mogami.
Direct Current is Your Friend
Instead of powering your stompboxes with a daisy-chain or wall-wart, consider using 9v batteries. Batteries provide a direct (DC) form of power over the alternating (AC) provided by plugging into the wall. This leads to a more consistent, even flow of power and many will say a better tone. It also frees up your pedal board from having to be X distance away from an electrical outlet.
Do you use a lot of stompboxes? Consider getting a buffer pedal to restore tone suck that can happen due to long cable runs. A dark or muddy tone can be an indicator of this. Without going into too much detail about buffers, beware that many pedals (like BOSS) have buffers in them. Adding more buffers won't necessarily hurt you, but it won't really do much good.
Some pedals sound great through the loop, especially time-based and modulation effects. Some loops are buffered, which can be another benefit. The sound can become much more defined when these effects are added post preamp, and the delay repeats aren't washing out that awesome preamp distortion.
Many beloved amps (namely tube amps) don't really hit their sweet spot until they're pretty cranked. Needless to say, this is not always plausible or possible to achieve. Consider finding an overdrive pedal that can get you where you want to be. Some of the higher-end ones sound phenomenal.
Another option would be to put an overdrive in front of the amp to push the breakup of the tubes more. This can be a compromise, as some gain can be acquired through the pedal, and some from the amp.
You can probably cut more bass frequencies from your sound than you think. Once the bassist starts thumping away, you will disappear.
Cut the Gain
Less distortion means more dynamics, a more pronounced and definitive sound, and less of a playing crutch. It can also help you cut through a band that has many players, or other instruments that are competing for your frequency range.
Play with Dynamics
Let the dynamics of you, as a player shine through. If you play with massive amounts of overdrive, distortion, or compression, the more of your dynamics are lost.
Don't Wash Yourself Out
Time-based effects can sometimes wash out your sound, especially in a band with instruments that compete for frequencies like two guitars, guitar and keyboard, and so on.
Read the Room
Every place you will play is different, from the sound reinforcement system to the physical dimensions of the space. Your overall sound will be up to the skills of the front-of-house engineer, but reading the room can help you tailor your effect settings so your echo repeats aren't being eaten alive.
Art is expression. If it weren't for the crazy dude who wanted to clip the hell out of a sine wave, we may never have gotten the first fuzz pedal. Break the rules and see what happens!