Which of these sites/apps you prefer for sharing your skill or work; WordPress, Blogger, Facebook, YouTube, Instagram, Tumblr, Twitter, Your website?

LinkedIn it is the most professional site to share your skills or work. 

It depends on the content i mean to share. Each one of these platforms offers something suitable for the kind of content you have.

I see that you're a freelance artist, here's what I'd do.

1. Instagram

Upload all your artwork here and generate hype around your work.

2. Twitter

Engage your fans through this platform and increase your visibility.

3. Youtube

Have you ever seen those "speedpainting" videos on youtube? People love them! If you're a painter then this is the best way to get recognition.

If not, you can also make tutorials on how you make your art.

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I'd do exactly that in that order.

I hope this was helpful.

Cheers

LinkedIN for jobs and summary, CV etc. Portfolio on own website.