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...
Thank you!