This is a rose from a reference pic on Google (you can probably google rose and find it fairly quickly. There are a few places I detest on it. I am only starting at this, and I chose a rose because well, there is a lot of shading. I don't know how to do highlighted areas though. yes I did outline the reference first but I did not do anything other than that.

Any pointers? Yes there probably is lots o' banding. I have not done the leaves yet, also.

In the future, attach the reference images yourself. It's nonsense that we should have to find an image to help you out.

You're completely not following the shading in the reference, and your colors are significantly different too.

The shading you have right now makes the whole feel flat, rather than volumetric. And keep in mind that flower petals are slightly transparent so light passes through. That's why (in the ref) the right-hand side doesn't have any really dark colors, but it stops at medium-red.

The colors need more contrast, and you're completely lacking the bright pink highlight. Your green is rather dark and blue, too. The ref has a bunch more yellowish in it.

In short, try looking at the reference more and understand how the lighting works, rather than copying the shapes and then make up your own shadows.

Try picking colors from the image, and see what they do when you ramp them as a palette.