You need to work out what works for which player, because it is based on their character.
My general approach is to use "You can win this game", "I expect a win", or "For the Fans" as a general team talk based on my chances in the upcoming match. Players with yellow or lower morale get "I trust your abilities", and for players where the option is available they get "keep going like last match" or "I expect better performance this time"
Then check with time what works for which player, i.e. some players will get discouraged if you want them to repeat their performance after a good match, others will get a boost. While in the match view, turn on the motivation screen and check how players reacted to your team talks.
In half time, players with a rating below 6.5, I tell them I'm disappointed about their performance, players over 7.1 get I'm happy with their performance, players over 8 get the absolutely phantastic talk. General team talk based on the current half time result, basically "I want to see more" if lying behind, Encouragement if it is a draw or a lead by one goal and Happy with performance if I lead by 2 or more.
If a player either missed or caused a penalty, tell them in half time to go out and show them what he can.
Sorry if the phrases don't fit exactly, but I'm using a translated version.