[instantpop]

To elaborate a bit on what RichUT posted, its all about knowing your teams strengths and weaknesses. Even more specifically, knowing what each player likes to do on the field. Keeping players in the right spots on the field and not getting fouls or turnovers with them seem to be the biggest factors in determining form as far as I can tell.

I've been playing as Spain in the WC mode lately. Sergio Ramos is my RB but he's also an offensive minded player. By default, he pushes up in the formation a lot, sometimes even getting as far up as a winger dumping in crosses. Pushing up and crossing with him actually gives him good match rating. Conversely, pushing Puyol up into midfield brings his rating down.

I've managed to keep all of my active Spain squad in the green on form just by getting to know the team. They also suit my more offensive style of play. When I was giving France and the USA a shot, I couldn't keep anyone's form in the green.

One other things I try to do is sub in people when I can, especially if one of my subs is 'on form.'

Hope that helps a little bit.