Reading how wet your brush actually is
Okay. Flat wash, graded wash, wet-on-wet. You've got water on paper and paper reacting to water, and by now you've probably noticed the same wash can behave completely differently depending on something you didn't think much about: how loaded your brush was when it touched the page.
This is the part nobody teaches directly. Tutorials show you the stroke, but they don't show you the fifteen seconds before the stroke, where you're standing there deciding how much water your brush is actually holding. That decision is most of the game.
Three wetness states, roughly
I think about brush-wetness in three rough buckets. Not official terms, just how I talk about it in my own head.
Dripping. You dip the brush, lift it, and a drop actually falls off the tip on its own. This is too much for almost everything except the wettest wet-on-wet work. If you touch dripping-wet brush to paper, you get a puddle that runs wherever gravity and the paper's texture want it to go, not where you wanted it to go.
Loaded but controlled. You dip the brush, then touch the tip to the rim of your water container or a scrap paper towel once. Not squeezing it dry, just knocking off the one drop that wants to fall. This is your wash brush. Most flat washes and graded washes want this.
Damp. You've used most of the water off the brush already, or you've touched it to a paper towel a couple times. This is for softening an edge, for lifting a little color back out, for that dry-brushy texture at the end of a wash where you want it to look a little broken up instead of smooth.
The mistake almost everyone makes at the beginner stage is loading the brush like they're filling a water balloon, then acting surprised when the color runs everywhere. Bless. It's not your technique that's wrong, it's the water math before the technique even starts.
How to actually check it, at home
Here's the practical part. Before you touch paper, touch your loaded brush to a scrap piece of paper towel or a spare corner of your cheap paper. Watch what happens.
If it makes a big dark blot that spreads fast, you're too wet. If it barely leaves a mark, you're too dry. If it leaves a clean, controlled stroke that doesn't spread past where you dragged the brush, that's your target for a normal wash.
Do this test constantly while you're learning. Every dip, basically. It feels slow and a little silly at first, tapping your brush on a towel forty times in one painting, but it's the single fastest way to build the instinct so you eventually stop needing the test at all.
Our dry air actually helps you here, weirdly, because mistakes show up fast. A too-wet brush in a humid climate might sit there being a problem for a minute before you notice. Here it announces itself almost immediately, the water either pools visibly or it's already start to dry at the edges while you're still deciding what to do. Pay attention to that instead of fighting it.
A confession about control
I'll say the honest thing here, which is that I am not a precise painter. I'm loose and wet and I like it that way, mostly because tight control is not my strong suit. Case in point: I once tried to paint my own hand as a reference exercise, sitting right there in front of me, actual hand, actual light, nothing abstract about it, and it came out looking like a catcher's mitt. Not a hand. A mitt. I've accepted this about myself. Landscapes don't have hands, so I mostly stick to landscapes.
I bring this up because reading brush-wetness is exactly the kind of control I've had to earn slowly, one towel-tap at a time, and I'm still not perfect at it. If your brush-wetness intuition doesn't click in one lesson, that's normal. It clicked for me around the time I stopped expecting it to click and just kept testing every stroke instead.
A word on cleanup and habits
Rinse your brush between wetness states, especially if you're switching colors, or you'll load water back into a puddle of the wrong pigment and get mud you didn't mean to make. Which, side note, mud you didn't mean to make is different from mud you're making on purpose. I'm on record liking a little intentional mud. Unintentional mud from a dirty brush is just a different animal, and it usually comes from skipping the rinse because you were in a hurry.
Also: don't leave a fully loaded wet brush resting bristle-down in your water cup between strokes. It bends the bristles over time and you'll be buying a new round brush sooner than you need to.
Before next time
Try the towel-test thing on an entire practice sheet, just wetness levels, no actual subject. Dripping in one corner, loaded-controlled in the middle, damp at the end, so you've got a visual reference for what each one actually looks like on paper before we build on it next lesson.