Right now I don't have a super organized tagging system, but I try to be consistent on these tag practices:

Has Likes/Dislikes -- if you activate this tag, you'll see what characters have slightly more developed profiles including a list of likes/dislikes.
Original Character -- if you activate this tag, you'll see what characters are not fandom characters. Note -- this excludes Muzikbots characters, which are both a fandom and an open species and as such are confusing.
For Sale -- if you activate this tag, you'll see all my characters that are for sale.  Currently I find it easier to put sellable characters into a folder and tag them rather than tag my characters who are not for sale, so you could also just check my Adoptables folder.
**New**
Sona --if you activate this tag, you'll see what characters are based more directly on me that may be more developed/mains as well
ArtFight -- if you activate this tag, you'll see characters who have entries on ArtFight.

I have a semi-organized folder system as well.
- Unsorted is for miscellaneous original and fan characters (mostly fan characters that I only have one in the fandom)
- Muzikbots Characters are for my Muzikbots and their partners -- open species/series characters
- Marvel Fan Characters are my fan characters for the Marvel Comics and Cinematic Universe.
- Kirby Fan Characters are my fan characters for the Kirby series by Nintendo and the Hoshi no Kaabi anime.
- Bionicle FCs are my fan characters for the Bionicle series (specifically generation 1) by LEGO
- Adoptables -- this should be self-explanatory, but there's a subfolder for me to place customs while I wait for the person who ordered them to claim them.
This list will be added onto and edited as time goes on and I work on my tagging system.