Pregame I let the assistant do it. Halftime if I'm winning I say I'm happy with the way things are going keep it up, if I'm losing I say I'm not happy and usually they are motivated. If tied it depends on who I'm playing, bigger team I just say we can still win this, lower team I say I'm not happy. Post game is pretty simple for me, win or draw(vs bigger team) I'm happy, lose or draw(lower team) I'm not happy. If we lose to a lower team or team of same level then I'm aggressively unhappy.
Using this method I usually keep a pretty high moral and even on a losing streak it doesn't get too low.