Below are a number of basic game tactics to help you in FIFA 11. You need to have some sort of structure in your play if you expect to win games. You can't just go out and pass around and shoot when ever, you need a planed form of attack and defence.
The Posession Game
If you possess the ball, your opponent does not, and therefore he cannot score. By possessing the ball with a series of smart passes, you can run down the clock if you are winning, or wait until you see the killer passing option through to your strikers and play them in on goal. If you can possess the ball and pass well, you don't have to be good at much else to win games in FIFA 11. Most concepts in FIFA are similar to real-life football, just look at how Barcelona play!
Utilize Fast Players
In FIFA 11, like other version of FIFA, speed is much more important than most other attributes. If you have a speedy player with the ball, you should very rarely turn down the chance to run into space. Strength is also important in FIFA 11, so even if your player is fast he may be pushed off the ball, so try to distance your player from stronger ones to avoid letting your run get cut off early. This is especially important down the wing (see below) when your outside midfielders or wingers typically have a lot of space to run at.
Consider Manual Controls
Although it is very hard to break away from assisted settings and play with full-manual controls, it is well worth it in the end. This is the same concept as mentioned in the skill moves section above; there is a tight learning curve but you'll be upset you didn't make yourself learn it earlier! Imagine if your shots and passes were 100% controlled by you. Of course, you would have no one to blame when you missed, but once you are proficient in manual shooting, you can hit corners consistently and thus score more goals. See more on the manual vs. assisted controls debate here.
Utilize Set Pieces
This one is sort of a given, but set pieces are one of the most useful things in all versions of FIFA. Because of the importance of strength and physique of a player, more so than previous versions, all set pieces used as a pass are golden scoring opportunities. Free kicks taken as shots are something you should absolutely not ignore. Once you get good you will score maybe 3 out of every 4 attempts, and that's a pretty good ratio, enough to make your opponent think twice about fouling you.
Create Set Pieces
This isn't exactly a strategy, but something you should take advantage of. New to FIFA 11 is the ability to create your own free kicks by designating runs to make your own unique play to surprise your opponent. From an angle where your opponent would expect it impossible for you to get a good pass or shot in, you could use a created set piece that is designed to create a scoring opportunity. It is very tough to make good, consistent set pieces, but I've seen it done very well before, so give it a try.
Take Advantage of Strong Players
If you have spent any amount of time playing FIFA 11, you may notice that the “all-important duo”, so to speak, is speed and strength. The best players tend to be strong, quick ones, seemingly regardless of other attributes. Take advantage of this on offense when you are playing with a team who has a big, strong striker such as Fernando Torres of Liverpool or John Carew of Aston Villa. When determining what the best method of attack is, consider giving the ball to a wide player who can make the run down the wing and cross it into your big striker. In terms of heading the ball, and many other things, strength rules all, and if the cross is good your big striker will likely get his head on it and put it away. Also try utilize your strong players when you need to hold up the ball and let play develop.
Mix it Up
This isn't really a strategy, but something to consider when trying to play a certain way. Although it is nice to have strategies and ways of playing which work well for you, you may be forced to change it up every once in awhile. Don't always use your wingers, try to posses the ball a bit or immediately try to play your forwards in for a chance to finish. This is especially important if you're playing online because human beings notice patterns better than computers do and will act accordingly.