I've had a few questions about tuning, so here's a video. Disclaimer: This is the method that works for me, but it's not the only one.
Around 30 years ago, I figured out what pitches I like best for my toms (C-G-D in descending order for my 10, 12, and 14-inch standard-depth toms) and a method to dial in those pitches consistently. Much of this approach is drawn from classical music training-tuning not only toms but also timpani.
Another great resource is DW's video on tuning: • How To Tune Drums - by...
In general, I focus more on pitch than on tension. Tension gauges can get you in an approximate range, but ultimately, you want the head to be in tune (at least with itself), which means listening for pitches.
Here's an extended version of the steps on the video:
1. Place the head on the drum evenly. Try to make sure there's about the same amount of head hanging over the rim all the way around the drum. When you place the rim on, similarly make sure the distance from edge to rim is uniform around the drum.
2. Tighten the tuning (or "tension") rods just until you start to feel some resistance. Make sure all the rods are heading straight into the lugs, and are not on an angle.
3. Now start to get the head up to pitch. Tighten each rod by the same number of turns. Work diagonally across the drum as much as possible so you're pulling the head against the drum evenly. Don't worry so much about the final pitch at this point, just try to get any uniform pitch.
4. Tap at each rod to hear the pitch on that part of the head. Fine-tune as needed.
5. Once the head is in tune with itself, start to tune it up or down to your desired pitch (if you have one). I use a tuning app on my phone, but you can also use a pitch pipe or any instrument that gives you the pitch. I like the app because I can just leave it playing as I work. The app I use on my iPhone is Cleartune.
6. Gently mute the middle of the drum and tap at each rod to hear just the pitch at that rod.
7. Hum or sing into the head at each rod and fine-tune. (Don't worry about your humming/singing! I certainly didn't in this video.) When that section of the head is in tune (with your pitch) it will resonate along with your humming. This is what I was taught to do when tuning (or checking the pitch of) timpani. The resonance isn't really captured on this video, but you'll hear it when it works. If you're having trouble with this, don't be a afraid to tune the rod down quite a bit and then slowly tune it up until you hear that resonating note-like "woooom."
8. Check the pitch with other drums. I tune my drums to fourths (like "here comes the bride" when going from low to high between two drums). Also check the bottom head. I tune the bottom (resonant) head to the same pitch as the top head. Other people tune it higher or lower. It's totally a preference thing. I use the same pitch because I like the maximum resonance with that fundamental note. I don't want any pitch shifts, and I want to minimize dissonance between the heads.
That's pretty much it. I tune before every gig and every recording, sometimes between every few takes. I almost always take the drums off their stands to tune. But if I can't (like if there are a lot of mics set up), I try to mute the bottom head with one hand and just focus on tuning the top head with my other hand.