@scribblstudios - yes... just one: PRACTICE... Do the tutorials @Rob2 mentioned - starting with the earlier ones on circles to get a feel for the tools (Inkscape, Illustrator, CorelDraw, whatever else you use to create vector art) and then start variations, different colour schemes, more complex shapes and eventually find a style you like (hopefully not just a copy of the angry birds art styel).
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Is the beginning of what has become the webs greatest ever series on vector art for games.