I don't know of any YouTube videos, but I will offer a tip that you should thin your paint and apply thin coats, building up the color. Generally, painting right from the jar or bottle, the paint is too thick. It will build up in thick layers, and they tend to show brush strokes more readily.
For water-based acrylics, I use a wet palette, and I recommend one. A wet palette consists of an air/water-tight container, a sponge, and a piece of permeable paper that is the actual palette. A wet palette helps ensure a good consistency to the paint, and you can also save a batch of colors over several sessions of work.
There are a couple of good brands of wet palette. Masterson has been around for a long time, and you can get one online or via art and arts-and-craft supply stores, like Blick's, Michael's, HobbyLobby. Redgrass Games also has a very good product, and their palette paper is very fine, finer than Masterson's. I have a Redgrass palette, because they brought out a small one, about half the size of a piece of letter paper, and I liked that smaller footprint. Masterson's is 8.5x11.
You can make your own wet palette, too. I made one, to test out using a wet palette before deciding to buy one. I took a takeout container, a kitchen sponge that fit into it, and I used brown packaging paper for the palettes. I might still use it today, if the plastic didn't wear and crack around the edge of the lid, if the sponge didn't tend to get funky, and if the paper didn't deteriorate relatively quickly and shed paper fibers into my paint. But it served its purpose.
For enamels, I thin with mineral spirits, and I use a ceramic palette for this. An old shot glass is just as good. I just put a little paint and a couple drops of the thinner in a well on the palette and mix it.
For Tamiya's acrylics, which use a lacquer-based acrylic carrier, I use their thinner, and I will either mix a bit of paint from the jar on the ceramic palette with a couple of drops of their thinner. Or I will pick up color on the brush from the jar lid or from the jar, then dip the brush into a small jar of their thinner, and let the paint and thinner mix on the subject. Both methods work for me.
I should add that some eyedroppers or pipettes are good to have, too. I prefer the classic glass eyedroppers with rubber bulbs, but there are inexpensive pipettes made of non-reactive plastic that work, too.
The point of all this is to lay down thin layers, as thin as if I had airbrushed them. Usually two passes gives me good coverage. I will brush in one direction in the first pass, then at right angles in the second pass. That eliminates brush strokes.
As far as the sequence of decals and paint goes, generally you'll add your finish coats first, then decals. You might still have some details to paint after decals, too, but generally, finish colors, then decals. Specifics may vary based on the subject.
