Few members have asked me about the canvas background I use to have that oil painting look. So, I think it's better to post in this section to share with others. Actually, the canvas I used should credit to Fashmir's contribution. Please see this thread posted by Fashmir.
Because it's very big PNG file, so Fashmir has posted a link to this file:
1) Put this PNG file under /resources/grain/ folder.
2) Click on the grain setting, then it will ask you to load a file
3) Select the Burlap_Grain PNG file
4) Then just adjust the roughness and scale you like
Then, I will set my oil brush pressure to 90-100%, 0% thinner, and loading around 90-100% too. You have to adjust according to your own composition and strokes.
Hope it's easy to understand.