It's interesting that the two main choices you've asked about are before or after the main entrée course. In my experience in England and in continental Europe (Spain, Italy, France etc.) the salad is served as a side dish alongside the main or entrée course and is intended to be eaten alongside this course sometimes in place of some form of vegetable dish.
The only time I've come across a salad being served before the main course is when it's intended as a starter to the main course, in which case you probably wouldn't then have a salad as a side dish.
I've never come across a salad being served after the main course, except as a fruit salad!
Perhaps it's a cultural difference between North America and Europe but if I was ever served a salad after the main or entrée course I'd be asking whoever served it to me, why and I would find it most unusual.