Here's a roundup of some interesting links:
How to Get Strong Outside of the Sagittal Plane - by Eric Cressey
For those of you not versed in the technical jargon of kinesiology, for movement analysis the body is divided up into three planes of motion (our world is 3-D afterall). The sagittal plane is most common plane to of movement and strength training exercise. It is motions that go front-to-back. Because the people who came up with the term don't know how a bow is held and shot (sagittal refers to Sagittarius, the Archer). A squat is a sagittal plane exercise because your knees bend front to back, as do the ankles and hips (more or less). A bench press is a sagittal plane exercise as well.
The other two planes are the transverse plane and frontal plane. The frontal plane is like a sheet of glass standing in front of you - motions that slide along the glass are frontal plane. So this includes an overhead press or pull-up. The transverse plane is like a table that you are sitting at, a motion that slides along the table is transverse. An exercise like the cable fly is a transverse plane exercise. (You may realize then that things are not always cut-and-dry: the bench press is both transverse and sagittal plane motion).
The article makes a good point about the need to train outside of the sagittal plane. Especially for lower body training - the focus of the piece. Furthermore the article provides a nice progression of exercises to develop strength and movement to the side.
While the article is very good advice, I would like to take a moment to insure that it's proper place in a program is understood. You should still do squats and deadlifts etc. Keep doing sagittal plane exercises as your primary exercises. Frontal plane leg exercises are used as a supplement. Something you do at the end of your workout, or as part of your warm-up. Or even just on the off days.
How to Hip Hinge Like A Boss - by Tony Gentilcore
The hip hinge is one of the most important aspects of the squat movement pattern. And it's vitally important to a healthy back in everyday life. But for many people this movement pattern does not come naturally. If you're not sure what I mean by hip hinge then just look at the videos in the link.
This article details a series of exercises to help a person train this movement pattern. Of these, the wall tap and band-resisted hip hinge are my preferred. But I'm sure that different methods work for different people.
Unlocking the Hips - by Eric Wong
A simple exercise based around an important concept - that of being able to dissociate movement at one joint from another. The specific exercise is to separate hip flexion from lumbar flexion. That is, lifting the leg while keeping the back straight, instead of bending forward while lifting the leg.
These two motions, of hip flexion and lumbar flexion, frequently get linked together by doing too many sit-ups - which are a crap exercise anyways.