An easy way to increase the eccentric (negative) loading is to do the concentric or lifting part of the rep with both legs, then the lowering part with one leg. After you hit failure with the single-leg eccentrics, continue the set by using both legs and a controlled negative.
Alternate legs on each rep. Make sure to do the eccentric portion in a controlled fashion to take advantage of the overloading effect. Don't just let your leg freefall when lowering the weight. Do 4 sets of 8 reps.
Breathing isn't one of those things we normally think about. Being the morons that we are – according to the general public, at least – bodybuilders generally prefer to devote our limited brain power towards things which seem more pertinent, such as calculating food intake or figuring out which tank top will make our guns look the biggest (okay, maybe that one's just me).
There’s no single best training tool. Instead of searching for one, increase the size of your toolbox. Here’s how to make your workouts practical and effective.