If you watch the Chris Cunningham "Director's Cut" there's a Bjork video called "All is Full of Love" (watch it on YouTube) where in the extras he describes the amazing lens flares used for the video. It sounds like it was entirely dependant on lens selection.
I'm a photographer, not a moving-picture type, and I know that in my experience older lenses, especially from before the mid-seventies, didn't have the glass coatings they do these days and lens flare was easy to achieve. If I know that need a flare, I'll rent an old lens with good glass and that seems to do the trick. If that's not an option because you're using a digital camera or something, I would suggest simply experimenting with the aperture of the lens. You'll get different types of solar flare shapes depending on where the sun is and how big the aperture is open to.
