The truth has to be told. No matter what happened in first half you do not have so much time. Something around 6-7 minutes is often not enough. In this article I will give my advises to use the time in efficient way.
Firstly, you came to the room with extremely tired people. Let them drink and rest for a while. It is a great moment to see if they have some observations. Be sure that very often they will start to discuss with each other, sometimes they will be mad or have pretension to each other. If it is not out of control it is good to let them talk to clear all misunderstandings. What is also important you buy some time to think and create a plan of your talk (you have some time walking to the dressing room, you should have some plan right? :)).
I choose 2-3 things that decide of the 1st half score. If we loose that situations I give (remind) how to resolve them in the game. For example we have tactics not to go 'active’ vs specific player but we do quite opposite. Or we plan to open the space for our playmaker to plan 1 vs 1 and we do not create that situation. If everything is fine I just remind about 2-3 most important things that are in our plan. What is more, I set the plan for the moment in game if we will loose and have to risk more (for example more active defense like 5+1). It is good not to waste the time out only for that and also not to have misunderstandings between us when the time come. Try to be as concrete as you can. Do not waste your time. This is not a time for: judging the players, personally evaluate everyone, talking 'philosophical’ arguments.
Should we be calm or aggressive? I do not know. I trust my intuition, and probably you should trust yours. There are no rules. As in pre game talk – you should be yourself. The arguments for being loud and tedious in my opinion are: when players do not fight on 100% in defense, to much incorrect individual mistakes (ideas) – to come back to tactics, to much relaxation (for example good result for us), when you see that players are in bad shape or extremely exhausted – to motivate them to find some energy to fight.
No matter what you say before 2nd half, the main goal should be to start 2nd half with energy and motivation. Even if you came to dressing room as broken fragments of the team you will leave it as a one collective.