It all depends…if you draw only a rose head, then you can relax and begin to draw it from any point because the rose head is the only object.
You can do it from the center, starting by drawing a chalice, or you can begin to draw from the outline contour.
Start from the central part by sketching a peanut-like or chalice-like noodle. The upper part is prolonged because it includes also the contour of one petal.
This will be the basic shape from which you will gradually develop the whole rose head.
You can gradually begin to add the rose petals. The rose petals open – fold outwards on the top of the rose head.
This is one of the typical features that you notice when you’re learning how to draw a rose head.
At this stage, the picture is a grotesque rough sketch rather than a drawing, but as you proceed the shape of the rose will slowly emerge.
When you draw larger petals, those petals that are opened, the rose head begins to get its typical shape.
So far we were sketching the basic contours of a rose head only by graphite pencil.
Since graphite pencil tends to make the paper dirty we shall replace it with a pink color pencil.
Using now a pink color pencil draw a single line over the initial graphite pencil contour sketch.
When you are ready, erase the graphite pencil lines. Graphite pencil lines will disappear but the pink-colored pencil line remains - weak, but remains.
So, the process of how to draw a rose will be a delicious coloring page-like work from now on.
You can start to shade the petals from anywhere you like. I would recommend shading very weakly first all petals only by pink color.
Shade first only the darkest parts.
Before you start to shade, observe for a while the ready picture. I would like to focus your attention especially on those parts of petals that are the brightest.
Those parts should remain bright when your drawing is finished, whatever final color you choose.
It is not necessary to philosophize too much over the “how to draw a rose” - process, nor over the shading of its petals.
Observe as carefully as you can and simply draw what you see.
I know it is easier said than done, but that is how it works. Every drawing is first and foremost a careful observation and study.
The more you sketch and draw (whatever) the more you learn how to observe better. That’s it.
Shade the whole rose head in pink color first. The pink color will be the basic layer on which you will build the next red color layer.
By the combination of pink as the basic and red as the second layer, you will obtain a kind of pink-red color combination that is closest to a real rose color.
Pencil strokes should always follow the direction of growth of the petals, which is from the bottom to the top.
Put as much red color as you feel necessary. There is no standard or prescription to this. You are the artist, you do the job.
Consider this exercise also as a good lesson to learn how to sketch and how to draw a rose.