Buy players early Monday after FUT Champions has finished or Wednesday when their price will generally be lower. Then sell Friday or Saturday when people play FUT Champions Weekend. Real life games can affect prices. If Aguero scores a hat-trick in a game his price goes up. So you can almost trade within games. Be aware of SBCs and always check player prices before you do anything.
Try to buy SBC players before or as soon as it starts. Before they go up. We will try to tweet any we think are coming. Basically any players in popular leagues rated 84 or over will rise in price if needed for an SBC. If you can store them.