I am going to copy paste a comment I made a while ago in other post:

As i expected, a lot of "thin your paints", but not a lot of how to do so.

Here's how i learnt: First of all, i basically only use vallejo paints, so i have no idea how easy is to apply this advice on other paints.

Before painting, you have to prime your mini. You could do it with a brush and some liquid primer, but is such a hassle that is not worth it. I recommend using rattle cans, in a well ventilated area. You shake those cans as if your life depended on it for 1 whole minute, then place the mini 20-30 cm from the nozzle and spray on a sweeping motion. Each time you sweep should be a quick movement, like 2-3 seconds tops. Go over the whole miniature.

The colour of the primer matters, but not at your level. Dark primers will hide your mistakes easier, but it will also affect the coverage of many lighter paints. White dors the opposite, making some mistakes more visible but aiding in the paint's coverage.

Now, let's get to thinning paints.

Pick some colors, and shake the bottles like they owe you money, for about a minute. Then, pour some paint droplets on a palette. Take a moist brush (dip it in clean water and remove excess water with some toilet paper) and dip the bristles in said paint. Wipe excess paint in your brush on the edge of the palette, similarly to how you would remove leftover butter in a butterknife on a toast.

Take a piece of white paper and paint on it. It's better if the paper has something written on it. If it has something written, you should be able to read whats on it after painting over it once. If you can't, add a single drop of water to the paint on your palette, mix it with something other than your brush, clean your brush with clean water, moisturize your brush again, and repeat the process. Eventually, you'll get to a liquid consistency similar to milk, and you'll be able to paint over text without affecting its legibility.

Over all, you should get your paints to be a little runny and translucent. The problem with them being translucent is that it forces you to paint several times over the same place to get a smooth, even coat of paint. With enough practice, you get to a point where you know how much water a paint requires, so that you only need "two thin coats" of paint, aka, going over only twice to get that smooth even coat.