The key factor to successful Visual Effects production is reference, reference and more reference. Take it from me, what's in your imagination is incomplete! Our brain is designed to compress out the details and only store iconic information. Developing your Visual Effects skill is more about learning to see than learning software. Forget what you think you know and try to look at the world again through new eyes.
...over and over again...
BBC Motion Library - A great site for finding motion reference. Well organized and searchable. They distribute stock footage, some free and some for a fee, but all is available for reference if you don't mind lessor resolution and perhaps a watermark.
http://www.bbcmotiongallery.com/Customer/index.aspx
