I only use Tamiya acrylics.
I use Tamiya acrylic thinner X20A.
I use enough thinner to dilute the acrylic paint to thin milk consistency.
Then I apply a base coat with strokes in one direction only, with the minimum strokes necessary. Don't worry, full coverage is not the goal here.
After that dries, apply another coat in the same direction.
After that dries, apply another coat 90 degrees from the first 2 coats.
This gives you 3 coats with an perhaps almost even finish. You can apply another coat in the original direction to finish.
If the part to paint is small, you only need 3 coats.
If the part is big and wide, you may need 4.
Recommend you spray either a gloss or matt coating to hide any brush strokes that may be visible.
Never use water with Tamiya acrylics.
You can also try lacquer thinner with Tamiya acrylics, but it's kind of "more" toxic than the Tamiya thinner.