Formations

Many managers put alot of emphasis on picking a team based on a particular formation. DONT DO THIS!! Always pick your best players and then select a formation which suits them. As mentioned elsewhere, it is more important to select your strongest team over anything else - including a formation. In my opinion ANY formation will be good against any other formation. Just put the best players in the line-up and use it.

However, if you have many options available for your strong team then its good to know that some formations do tend to work better against other formations. This is explained below:

4-4-2
This is an allround formation.
Countertactics: 4-4-2 if your skill and form is better, or 4-5-1. Check if your opponent favors pressure.

4-5-1
Strong defense and midfield, weak attack. More offensive than 5-4-1, see below.
Countertactics: 3-5-2 could be a good answer to 4-5-1. Three defenders beat his lone attacker. Other options: 4-2-4 long balls or 5-2-3 / 4-3-3 long balls. Evade the midfield battle and shoot every intercepted ball from the defense to your strikers.

4-3-3
Allround offensive formation. Good if your midfield is strong.
Countertactics: 4-4-2.

5-4-1
Very defensive formation.
Countertactics: 3-4-3

3-5-2
Very offensive midfield formation.
Countertactics are: 4-5-1 / pressure (try to beat his midfield), the 4-2-4 long balls or 5-2-3 / long balls (try to evade his midfield); or 4-3-3 / long balls. (in my personal experience, 4-3-3 long balls had disappointing results, however much depends on the relative strength of your midfielders and forwards)

4-2-4
Defensive counterfootball formation. No midfield. Often in combination with long balls.
Countertactics: 5-2-3 / pressure with headers in your team might work.

3-4-3
Very offensive formation, strong midfield, very strong attack.
Countertactic: 4-4-2

5-3-2.
Defensive. Personally I prefer 5-3-2 when trying a defensive formation.

Remember that if you play defensive with a lot of defenders, defending is the only thing your team does. Thus, its important to maintain a balance between formation and style of play. If you have a defence formation like 5-4-1, then you should play offensive; 4-5-1 normal; 4-4-2 cautious etc. Basically, managers should play offensive with a defensive formation and defensive with an offensive formation to maintain that balance.