Language Matters
How you and the other adults involved in your team talk to your players (what you say, how much you say, when you say it) can clearly have an enormous impact on their performance and enjoyment of the game. A few interesting points on this subject...
Praise
When I first started coaching a team I assumed the players needed lots and lots of praise. Everything they did was "brilliant", "outstanding", "superb". They were "fantastic players", "really skilful" and so on. My logic went something like praise = confidence and confidence = better players and that logic wasn't totally flawed (nobody is going to have much confidence if they're getting negative feedback all the time), but there has been some very interesting research around this topic and it turns out the type of praise you're giving can have a huge effect on your players' effort levels and perseverence and that praising targeted effort rather than "inate" ability is far more effective.
There is a well known study on this by Carol Dweck (author of Mindset), who (in a nutshell) split a group of children into 2 groups, gave them the same maths problems to do and then praised half for their effort levels and perseverence and the other half for their ability and results. When given harder maths problems to then do, the group praised for effort continued to try for much longer than the group praised for their ability, who generally just gave up. There's a bit more to it than that, but that's the gist of it.
Rather than me waffle on about it, this information about the Carol Dweck praise/mindset study covers the topic very well...
And to understand it properly, it's also worth reading this follow up article published here...
How might this sound in a football context? Well a comment like "Dan, you're such a brilliant player, you're skilful and you always score such good goals" as opposed to "Dan, I love how hard you worked today, your effort levels were fantastic and you earned those goals you scored" are both praise, but the second comment is far more likely to send Dan home wanting to keep working hard to improve further.
Praising for what someone did ("Your 1v1 defending was outstanding in today's match") rather than what they are ("You're a brilliant 1v1 defender") has also been shown to be far more effective. The first comment praises something that happened today, but gives no guarantee that will always be the case. The second comment is telling the player they are a fixed something (a brilliant 1v1 defender who has already "made it" in that respect) and nothing is going to change that. The ramifications are obvious.
Similarly, telling someone they're inately not something, for example "just not a striker" is cutting off a whole section of their development. I heard a coach from another club telling a 9 year old kid he had to always play in defence for exactly that reason, which is clearly ridiculous at that age. Just ask Dion Dublin.
So the language of praise and how it might affect your players' development in the long term is something that can be incredibly powerful.
Criticism and Mistakes
Criticism is always going to be a difficult thing to handle. There is absolutely a place for constructive criticism when teaching anything, but used in the wrong way it can be devastating. Again, it comes down to tone, language and the type of criticism. It also comes down to knowing your players and understanding who will benefit from different levels and types of critique.
An approach of "how could you do that differently next time?" or "what might you change if you were in that situation again?" where you can then demonstrate or discuss the situation and how to learn from the mistake is likely to be much more effective for most people than a direct criticism that just tells the player that what they did was "wrong" or that they can "never do that again". Subbing someone off directly after a mistake is also likely to have long term effects for that individual. As hard as it might be, unless they're in tears and need calming down, letting them stay on the pitch for a while is likely to help them get over their mistake a lot quicker.
Setting up an environment where the whole team understand that everybody makes mistakes and that we use them as a learning opportunity to help all of us improve will stand you in good stead when looking to then address these sorts of issues further down the line.
Pressure
The language we use can have an enormous effect on the pressure the players feel they're under. We all know that intense pressure is likely to lead to jittery performances, but it's a fine line and it comes down to knowing your players. Some may thrive under pressure and if you genuinely feel that's how you get the best out of your players then it may be something you want to use. Again though, I'd say this would only be relevant at the older age groups. Having 8 year olds under intense pressure to win is likely to have only one outcome.
The worst I saw was an U12 coach who told a player, absolutely seriously, about to take a penalty to save a draw in a game "if you miss this I'll kill you". He missed.
A Wake Up Call
Does all this mean you never raise your voice and that everything is super happy-clappy the whole time? That depends on your philosophy, but I would say no and that in the older age groups there is absolutely a time for a more direct approach.
I'm generally very positive with my players, but I have absolutely had a number of times where I felt the right half time team talk involved me giving them what I would term "a wake up call". Used sparingly and for the right reasons, this can be powerful. If you do it every week it just becomes white noise and if you're doing it just to let out your own frustrations, it's unlikely to be particularly focused or useful. Sometimes you just have to take a deep breath and count back from 10 before addressing the players!
Sometimes Saying Nothing is Best...
To use Ronan Keating as inspiration (really? - Ed) I've found that on occasion it's worth considering the idea "You say it best, when you say nothing at all." The most effective half time team talk we ever did involved the coaches very much taking a back seat. 2-0 down to a team we should have been beating comfortably and with every player putting really low effort levels in, we just told them it wasn't good enough and they had 5 minutes to discuss amongst themselves how they were going to sort it out. We didn't listen to what they said and to this day I still don't know. They decided amongst themselves what was wrong, what needed fixing and they went out and won the game 4-2, with every player giving 100%. Giving ownership to the players rather than talking to them yourself can be a great approach, again, if used sparingly.
Similarly, on the sidelines, if you can avoid coaching too much whilst the kids are actually playing, you're helping them improve their problem solving skills far more than the coach who micro-manages every player through every single thing they do. We used to come across a coach like that and it was like he was playing a computer game and his players were robots. And his team generally lost because the players made lots of mistakes, which were then loudly criticised from the sidelines by the same coach.
If you absolutely have to talk during the match, phrases like "where's the danger?" or "what could you do now?" will allow the players to still use their own brains rather than be puppeteered by you, but try to make sure you aren't giving any instruction to a player who is actively involved in a decision-making phase of the game at that moment. They have a picture in their head, based on what they can see. Having you shout "SHOOOOOOOT" when they're in the vicinity of the goal is just going to put them off. Same for passing, tackling etc.
Even better if your players can help each other on the pitch by giving targeted advice, without you having to do it. I would much rather have my centre half telling his central midfielder that he should drop back and cover than for me to be doing it. Lots to think on.