I think the first step should always be an Art Portfolio,
because businesses that sell art online for you, will ask to see it.

And I think it should be consistent in some way,
it should say: "This is what you can expect from me."

You should start simple,
but you don't have to keep it simple.

Start with 3 self portraits,
in impressions style.

Do 3 pieces,
in photo realism.

And three illustrations,
simple, cute caricatures.

I love Pop Surrealism,
so I would make photo realistic caricatures.

But you can do any technique,
though you may need to do 3 works per technique.

Search Dribbble for face illustration
to get an overview of different styles.

Search the internet for best art portfolios,
to see what other artists are up to.

Art is a culture,
and looking over other people's work helps you join in.

And know that you will want to change things in the future,
so you'll probably end up uploading files again somewhere.

The portfolio is a pretty crazy thing,
because once you set it up, you'll never fall lower.

Whatever your future holds,
you will always start as an artist.

Well into your future, your portfolio will make your heart smile,
and maybe cry, as you teleport yourself back to your youth for a moment.

Beyond the basics, search for frame on Unsplash or maybe billboard or advertisement,
and slide your artwork in there.

And you can also try different things on the subject end,
rather than using your own portrait or "Reddit Gets Drawn"...

Get some flesh colored polymer clay and rough out some characters,
take the photo and use it as shape and color reference in krita.

Although portraits are probably the quickest way,
to show how realistic your art is.

Urban life scenes, Nature and Still life photography,
are also a great source of color and shape for your paintings.

And you can grab an Action Figure Drawing Model,
to use as reference as well.

The standard wooden mannequin and hand,
actually go together, you pose the mannequin first...

And once you ready for hand details; you pose the hand to fit your mannequin pose,
take a bunch of photos and splice a unique scene together with tone and shape reference.

Learning blender, or 3D modeling in general is another source of tone or shadow,
and programs like MakeHuman will help you with posing your characters.

Overall, whatever you will focus on,
will teach you how to do it well in no time.

Painting faces with the aid of Krita's Image Reference tool, and reference images covering the entire canvas,
will teach you the features of a face in a way no teacher can.

Digital painting is extremely advanced,
not many artists get it yet.

If becoming a professional artist is the aim,
using reference tools will enhance the quality of your work.

It will protect you from ever getting stuck,
and help you get all the details right; the first time.

You can use a grid to transfer photo onto a real canvas,
but using a grid on your computer, is just adding extra steps to a simple process.

Digital art it helps you with color and shape,
so that you can innovate beyond it.

So that you can do things that would be too difficult or impossible,
on a standard canvas.

There are so many directions you can choose that it is impossible to make useful recommendations,
move slowly and take to things that call to you; and you'll invent a whole new universe, in no time.