I know I've been having trouble with my psoas muscles recently. It's a complicated problem that I've only just discovered...and am working to fix.
The basis of all injury is misalignment and incorrect usage. Technically, if you knew every inch of your body perfectly, you would never injure yourself (except for accidents that involve things/people other than yourself, of course). Strengthening and toning is an important way to prevent injury, but you also have to strengthen the right muscles.
Which brings me to this post on another blog that was sent to me by my lovely ballet teacher: Getting Higher Extensions! by Deborah of The Body Series blog. Strengthening the psoas muscle is not only easy and fast (10-15 reps every day for 3-4 weeks for results!), but is a sure-fire way to get your leg higher in developpes! I know I've been struggling with getting my leg past 90 degrees for a long time in front extensions, and with the problem I discovered earlier with my psoas muscles, this makes a lot more sense. I'll be adding this to my daily strengthening routine, will you?
As a side note, I've taken a quick glance at the rest of this blog, and it's brimming with excellent tips and advice on just about every topic a dancer could wish for, from a neuromuscular educator (it's her profession)! If you've got a certain issue or goal, take a look at her categories in the bottom right hand corner of the blog. You're sure to find some stretch or advice that will help you get there!