In your role as a soccer coach, you need to communicate effectively with a lot of different people: your players, parents, grandparents, officials, other coaches, etc...

All of them have different agendas and need communicating with in different ways.

The Players
Communication with your players goes far beyond simply giving them instruction. If you took a communications class in high school or college you will remember that more than 50% of communication is non-verbal. Facial expressions and tone of voice also convey a great deal of the communication. Leave the sarcasm at home! Players may place a great deal of importance on anything you may say or do, possibly more than what their parents may say or do. Also, although it can be tough with 12 jabbering kids, try to listen to each one, allowing each one to talk in turn.
A few pointers:

1. Talk to the players' on their level, both physically and emotionally. This may mean getting down on one knee and looking into their eyes as you communicate. Use simple, direct statements that will be less likely to be misinterpreted.
2. Don't wear sunglasses on the practice or game field. Players need to make eye contact with you to fully understand the communication.
3. Be positive, honest and sincere with your players. When trying to correct a particular skill problem, it can be advantageous to make the mistake yourself, and then point out your own shortcomings. Players will respect a coach that is honest. Be positive: constant 'nagging' will only 'turn off' your players'.
4. Tell them what you want to tell them, tell them again, and them tell them once more. Try to reword your communication each time. This will give you a much better chance of getting the communication across with ALL the players.
5. Be loud enough that all players can hear you, but don't scream at them. Clearly understood voice communication will get their attention and your respect. TIP: In one-on-one communication, a whisper may serve the purpose and be much more effective than a normal or loud voice.
6. Avoid inconsistent or confusing body language. I.e. don't turn your back on a player talking to you, expecting praise, attention or instruction, Shaking your head while telling the player "nice try"...

1. Listen
2. Listen
3. Listen

They may be concerned about their child's skill development. i.e. "Johnny makes a lot of goals, but my kid...". Just be positive about their child's development unless you too have a concern that their may be a medical or physical condition that needs attention.
They may think you're a lousy coach, or you just haven't developed a relationship with their child. If they're wrong, try to rectify the miss-communication, but not at the expense of the team. It could just be the parents or child's problem, and you probably can't "fix it".
Finally, if you need to talk to a parent, do it after a practice or game where you can speak to them without the child being present. Sometimes a phone call or e-mail will work just as well.

The Officials
Maybe it works for Alex Ferguson, but it won't work for you. Yelling at or disagreeing with the coaches will solve little during a game. What it will do is show your players that you are disrespectful of the officials, and they will tend to do the same. If there was clearly a bad decision, bring it up after the game with the official or later at a specially called meeting.

The "Other" Coaches
Make an effort to seek out and greet the other coach before the game. By establishing an acquaintance, you may be able to accomplish more together than alone. For example, at the first game of the season, you may have some new players that can't play an entire half. It is very likely he has the same situation. So the coaches decide to have 'unlimited or free' substitution. Like the official is going to argue with BOTH of you! I don't think so. In most associations that tend to be non-competitive, the two coaches can then determine the best use of the rules for "THIS" game.