1. Build sets rather than buying the card outright unless the card is trading below set value (e.g., Hampton in the Breakouts).
2. If you do buy LTDs, usually wait until they're about to leave packs (unless there is a special offer that floods the market like at Halloween).
3. Selling off the team (and moving to BNDs) prior to about 5 days before an OVR increase will generally preserve the coin stack so that you're not always trying to refill the bank.
4. Don't chase unreasonably expensive cards (generally more than 3M coins) like H2H ranked cards.
5. If you spend money, go after packs that return more than 100k coins per $10 spent (like the weekly platinum packs).