When serving soup and salad together it's best to serve the soup first so that the soup can be eaten before it gets cold.
Traditionally the soup is always served first as a warm soup and then the salad is served last.
However you can serve both the soup and salad together and the person can decide which to eat first.
I always just serve the soup and salad together and allow the person to decide what to eat and when to eat it.
Most people do eat the soup first and then the salad afterwards.
Also what I like to do is add some of the salad to the bowl of soup and eat it that way too.
Then I finish eating the rest of the salad after I eat the soup.
You can also use leftover salads to add to soups and make a soup salad which is also delicious.