It's hard to prescribe any particular exercises that would be most beneficial for you from your description. The "long leg--short leg" thing can mean many things, although you are right that it almost always refers somehow to the fact that the inside and/or uphill leg is typically bent more than the other leg. It's an important concept, and on some levels, almost inevitable. It has become almost a "buzzword" in some circles, though, and I'm always wary of things like that, because they can become way overused. I know at least one instructor who seems to believe that "long leg-short leg" is some sort of panacea for whatever ails you.
I'm not trying to say that the feedback you were given was not appropriate for you, though. But it is hard to say at this point exactly what it meant, or exactly what the perceived problem was that "more long leg-short leg" should cure. I will suggest that it often refers more to a timing issue than an actual movement (no idea whether this is relevant to you, though, so take it for what it's worth!) Like many things, what happens in one turn must reverse for the next, and the timing, rate of speed, and intensity of the movements involved can greatly affect the transition of the turns.
Can you describe any more? What do YOU think the issue that prompted the feedback was?