For example a skull can be broken down into 5 circles, a square and triangle, 1 circle to make the dome of the skull, 2 smaller circles to make the sides of the skull where the eyes would be, 2 even smaller circles to make the eye sockets, the square to make the lower section with the teeth and then the triangle for the nose area.
Now that would not give an atomically correct skull but it would give you the basic shape from which you could then use as a foundation to paint a more impressive looking skull, but that is the point, when you build a house you start with a foundation from which you build your house not the roof.
Another basic; but possibly most important, point is thin paint and this is true for painting in general, not only will thick paint will show brush strokes but there is the point I like to make of "you can always add more paint, you cannot take it away", so having patience is a must; or a hairdryer, as there will be many instances where you will be waiting for paint to dry.
Finally unless you have an eidetic memory or you have painted so many of the symbol that you are pro at it (if the latter is the case why the fuck are you even reading this, go do something constructive with your time) having a reference image can be a god send. This works for not just pictures but freehand script, printing out what you intend to "write" with your brush to the correct size and placing it above where you are painting it helps with correct placement of characters.
It is also worth noting that freehand is merely a culmination of a succession of lines, if you can paint a simple line to a specific size and length then there is absolutely no reason you can't knock out basic freehand, no excuses!
Now all that said I am not going to paint a skull, I like to be wishy washy and not make any sense, deal with it! I will do a skull when I eventually get back to my Exorcist Space Marines :P
Instead I am going to paint the Legio Invigilata symbol, but it shows the principle of thin paints and a plan.
So the base image, I break this down into a cross, 4 circles, an oval, and 12 triangles. The lightning strike I tend to just do as someone with a Steel Legion it is pretty much done without thought.
So to start with thin white paint I sketch out a cross. As the main shape is a compass a cross seems the most logical starting point.
The sketch out a circle, don't worry about being too precise there will be much in the way of correcting throughout the process,
Now just more and more and more layers! REMEMBER LET THEM DRY!
So now we have the cross and the circle time to add in the triangles, Starting with those at North, East, South, and West. I do these with 2 pull strokes to draw the sides; pulling the brush away from the point towards the circle, and then filling the in the body of the triangle. The reason for the stroke being a pull stroke towards the circle is not just some random shite, the paint will pool at the end of the brush stroke usually so if you do your pull stroke towards the tip you will be left with a little white dot rather than a sharp point......now I know that sounds like an euphemism but entirely innocent clean your mind out!
Now the same is done with the 8 lesser points, again 2 pull strokes to form the triangle and then fill in the body.
So we have the basic shape of the compass. Now for the rest, the red circle containing the eye actually sits inside a black circle, so first we need to paint a black circle, carefully sketch out in thin black paint the black circle, if you are not confident with this start the circle small and increase it's size gradually, it is easier to draw a smaller circle and increase rather than go balls deep in the massive hole......innuendo central! Again start thin and build up the layers
Now inside of the black circle paint the red circle, I start with a dark red thinned to get the shape.
Build up the red in progressive layers. Oh and I added in the lightning strikes
Now for the eye. Within the red circle carefully paint the white oval, using thin paint and building up the colour in layers to you have a solid white.
It took me about 2 hours to paint that and 4 others on the various bits of knight carapace.
Practice is key here, more you paint the more dexterous your fingers will become, the more dexterous your fingers become the easier it is to paint, the easier it is to paint the more you will want to paint