The team talk before the game should reiterate what you want to accomplish. This may differ based on the opponent. You may be able to impose your will on some teams and you may have to make adjustments for other teams from the start. There will also be teams that you match up evenly with, so you want to stress execution of individual and team tasks. A very young team may need some motivation from you. An older team needs more clarification of function. Every player must know what he/she has to do, so that the team is functioning as a unit.
Let me give you a couple of examples. You are playing a weaker team, so you decide to win the ball higher up the pitch and take the game to them. You may want to ensure that the players know where your line of confrontation is set and where you want to force the other team to play. If the team is not very technical, you may try to force them to play up the middle through traffic. You may also want to pressure the full backs to force them to give the ball away close to their goal. You can play with an extra forward to help with this.
If you are playing a better team, you may want to clarify that you want to sit back and counter. Protect the space in behind you and communicate to the players how you wish to accomplish this. Maybe a five man midfield with wingers to facilitate an early diagonal ball on the counter. You may also want to employ a very strong target that can hold the ball for a few seconds to give the trailing players time to join the attack.
As far as half-time goes, you should think about adjustments if your plan is not working. Players not performing to potential(substitutions in the second half or immediately) Keep your talk concise. Too much information has no impact. Three areas of concern to adjust as a team is plenty. You can, however speak to the individual about how he/she is performing and what they can do better to help the team cause.
As you can tell, there is nothing specific you have to say, but you have to read the game and make adjustments accordingly. There may be times when you have very little to inject, because the team is playing well. Other times, when it all seems to be going wrong is when you have to focus on the major points of emphasis. You can’t fix everything at half-time, but you can change the game with key adjustments.