The most perceptible impacts you can make without actually getting a different camera is lighting and sound.
<em>Sight, Sound, Motion: Applied Media Aesthetics</em> by Herbert Zettl is a great resource on this front. Understand single and multipoint lighting. Understand sound recording/design. Understand the way these all fit together... and treat every project as more than casual videography, because if you're not using the camera, lights and sound to do something more than just give us a picture to accompany words, then you're not utilizing the medium or the bandwidth and you may just as well be sticking with audio.
On editing, I would pick up any book on the basics of Non-Linear Editing. Youtube tutorials are helpful to give you some hands on practice but the more you understand about the fundamentals of video, of lighting, of sound, of editing, the more versatile you'll be... rather than having to keep going back to YouTube to look for things function by function, step by step.