-Using my art for personal icons, banners, avatars, etc- all fine. You don't need to ask. Give credit somewhere if possible.
-Using my art for DND campaigns- fine.
-Using my art for personal lockscreens/wallpapers- fine.
-Using my art as reference, inspiration, even for credited direct copies; all fine.
-Credited reposts off-site; fine.
I do not answer emails or notes asking if my art can be used for these purposes. I get too many. Please just go ahead without asking.
Now for the NOs:
-Do NOT sell my art.
-Do NOT use my art for commercial gains without a license.
-Do NOT use my art for commercial advertising without a license.
-Do NOT repost my work without credit.
TL;DR: Just don't be rude. I'm really very lax about my art being used for personal things, that doesn't bother me. Just don't try to profit off of it or share it without my name attached; that's really it.