Sometimes you just have a bad season - overall, injuries seem to be about right. Some teams have horrid streaks while other have none at all. It averages out though. Put most of them down to bad luck.
If it's the same type of injury, have a look at your training regime. Might be something there which is not right.
If it's players coming back from injury, are they actually fit when you play them in a first team game? Reserve games are ideal to get players back up to match fitness again and so making it less likely you'll see them injured quickly again.
Always check the fitness of players - tired and unfit players are more prone to picking up injuries. Just the way it is. So pace your players, give them rest and breaks from games during the season if you possibly can - missing your top player for a meaningless midweek game is far better than playing him when he's jaded and tired and seeing him pick up a strain which puts him out of the cup final... (edit: a lot of people who play Arsenal report this problem - are they overplaying those youngsters I wonder?)
