Below are some YouTube channels or other online tutorials that may help you to develop your skills further. 
Click on the image to go to their website.
Realism:

Michael James Smith: Realistic landscapes

Mark Carder (Draw Mix Paint): realism in oils

Wilson Bickford: Paint landscapes

Kevin Hill: Oil and acrylic landscapes

Expressive:

Farbi Flora: Expressive painting techniques

     
Have you come across a really good online tutorial? Let us know about it here...
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