In case you are looking through my collection and think it is a confusing mess (e.g. how can he both "Own" and "Want to Buy" so many games), this is how I organize and tag my collection:
Owned: I use this tag to mark games that I own, I have a PnP copy, or can cobble together (with a deck of cards, for example), that I would be interested in playing when looking for a game from my collection to play. I leave expansions out of this category, unless they are for all intents and purposes their "own game". For example, I play Dominion with expansions mixed and record my plays only under "Dominion", so only Dominion is marked as "Owned". Something like the Korea Power Grid map is effectively its own game (even though it uses parts from the main map/game), so it is marked as "Owned". I use the category in this way so that I can use tools/websites to suggest games to play based on number of players, play length, etc.
Previously Owned: Games listed in the BGG game database that I formerly possessed, but have sold/traded/given away. If I had owned a game but never played it while it was in my possession, it does not get marked as Previously Owned...because it was as if I never owned it in the first place.
For Trade: Games that I no longer want to own, and are available for trade or purchase. Or games that I am *thinking* about getting rid of, usually because they are not getting played.
Want to Buy: Games that I own an official published copy of. I don't include expansions in my "Owned" category, but these would be included here. This category reflects all games/expansions that are part of my "true" collection, and helps me determine what games are eligible for selling or trading.
Want to Play: Games that I have come across that look interesting that I would like to play and/or PnP, and games I own that need to get to the table.
Preordered: I use this tag to mark games that I have PnP'ed (i.e. I technically "own" it, but not the real game).
Wishlist: Games that I am interested in buying (level of interest given using the 1-5 scale for wishlist items).True Collection (Owned Games, Minus Expansions, Minus "For Trade")Owned Games (Including Expansions)Playable CollectionUnplayed GamesNot Yet RatedPlayed "Want to Play"Want to Play
I am also moving towards a simplified rating system (5 rating categories) that should align with the BGG rating system, but leaves out the precision and minutiae that I don't have the time or wherewithal to engage with. "What makes game X a 7.5 but game Y an 8?" I don't realistically know how to classify games down to that level of detail, nor do I want to take the time to determine that. Here are the 5 ratings:
2: Bad. Just bad. Not "just not my cup of tea" bad, more like "anyone who enjoys this has something seriously wrong with them" bad.
4: Not good. I don't really ever want to play this game again. I don't begrudge anyone for liking it, it's just doesn't do anything for me or is potentially mildly irritating. If you REALLY want to play this game, I'll probably try to suggest something else, but ultimately I'll play it with you 'cause that's the kind of guy I am. Damn you and your puppy-dog eyes...
6: Average game. This might be a game that is perfectly fine, it just doesn't offer anything new or different compared to other games. As I age longer into this hobby and have played more and more games, most games seem to fit into this category. If that is the case, I don't feel the need to own the game, but I would probably play it if you really wanted to. Or it might be a situational game that sometimes I feel like playing, but sometimes I don't. A lot of filler games would probably fit into this category. So yes, I even own some of these "average" games.
8: Darn good game. I would probably like to own it, although the desire to keep my collection size reasonable combined with me knowing other people who own it and like to play it could prevent that. It would probably be rare for me to turn down a game although -- my mood/energy level/having played it too much recently/not having the right players for the game/not having enough time to play it -- might cause that to happen.
10: Superb game. If I don't own it, I surely need to. I can't think of any instance when I'd turn down the opportunity to play this game. Rare rating.