Violin concertos

For those of you who have written violin concertos (or any other piece for violin and orchestra), how did you go about doing it? How did you write the orchestration and the solo part so they could fit in together?

I've listened to a lot of them, and different composers orchestrate very differently, I think. Bartok's 2nd Violin concerto, for example, has pretty transparent orchestration that lets the violin shine in solo parts and lets the orchestra play great passages while the soloist takes a rest. Shostakovich's first, though, lets the orchestra play with the violin a little more.

I'm just wondering how you all do it. (or, how you think you would if you did.)