Generally, I only trade normal cards from a game once I have amassed enough cards to create 5 badges. So if a game has 5 cards, I start trading once I have 26 cards. That way I know what I need and what I can trade away. An exception is if I have like 9 of one card, it's obvious I can trade a few off while waiting to get the rest. I very rarely will break a set. I also rarely trade if there will be a hold on the trade. I trade 1:1 same set only, except cards I already have a level 5 badge, then I am willing to cross-set trade if you have a card I need. Foil cards I will trade all of them, unless it is a full set. Booster packs I will only trade if I already have a level 5 badge for that game.