Many guitar players, including myself, have struggled with finding a good tone. After digging around and doing some research I've tried changing several things on my guitars and amps that make a much bigger difference in tone than you think.
1. Do NOT Scoop Your Mids (Yes, I know lots of people will already know this)
Even if you're playing metal, try turning up your mids to at least 12 O'Clock, it sounds a lot punchier than it would with them all the way down. It makes your tone much tighter playing an genre of music.
2. Raise the Action on Your Guitar
Strings make sound by vibrating, so the lower they are to the fretboard, the less space they have to vibrate. Even though it's easier to play, it's worth trying higher action. It gives a fuller, louder tone than lower action, and it will make you a better player by having to get used to the difference.
3. On Guitars With Tremolos, Take off the Plastic Cover on the back of the Body
It's really hard to explain how this makes the tone better, but it makes a huge difference. My guess is that it allows the body to resonate more. Whatever it does, it makes your guitar sound better, and if it makes your guitar sound better, why question it?
4. Experiment with Different Pickup Heights
This will differ with most people depending on what pickups you play with the most. For me, on my Strat I pretty much only use the neck and bridge pickups, so I raised them and lowered the middle, which is where I pick. This gave me a volume boost and less picking noise because my pick didn't hit the middle pickup.
5. Invest in a Tube or Hybrid Amp
Pretty much any guitar player will tell you a tube amp sounds better than a solid state. Even if you don't have the extra cash to spend on a tube amp, you can get a great hybrid amp (an solid state amp with tube preamp) such as the Vox Valvetronix for a lot cheaper, and they sound amazing for the price.
6. Invest in Higher Quality cables
Spending more than $50 on a cable may seem outrageous, but it's well worth it. Not only do they last longer, but they're not as noisy as cheaper cables. Many are a lot harder to break, and come with warranties that allows you to replace them rather than spending more money to get new ones whenever you break one.
7. If you play with lots of gain, use a noise gate.
Even if you're playing clean, a noise gate helps if you have lots of pedals. Plus, if you're playing live, the louder you are, the more chance there is you'll get feedback/distortion when you don't want it, so it doesn't hurt to have a noise gate one to keep the chances down.
8. Change Playing Techniques
Where you would usually play legato, try alternate picking, where you would usually slide, try bending, etc. A major one that I've tried that makes you sound like a completely different player is not using a pick and only playing with your fingers. It gives you more ways you to hit each note, and it makes your playing more diverse. Change things up, and you'll be surprised with what you find.