Don't work too dry, but do not use too much water.
The shape, width and quality of the brush are to a great extent qualifying the effect you can achieve with it. For instance, round brushes are ideal for making curves and drawing curls.
You draw straight lines preferably with a flat brush, keeping the handle of the brush pointed in the direction of the line. To draw a thin line, you do not necessarily need to use a narrow brush. You can also use the edge of a flat brush for that. This brush is also very convenient for making a thick line merge into a thin one, turning the brush on its side in one fluid action as you go automatically changes the line from thick to thinner.
When you come to the end of a line, lift the brush from the skin in a single smooth movement.
Hint: to make beautiful, thin lines, you mix the Water Make-up with Cleansing Lotion instead of water.
If you do not want the colours to mix, be sure to wait for the first layer to dry before applying another colour over it or up against it.

Hint: Regularly change the water you rinse your brushes in and preferably work with two water bowls: one for light and one for dark shades.