I adore how they are modest because of their loose gathered look and how they have a little vintage flair to them, plus I think that they are pretty versatile to use for many looks such as Bohemian or Steampunk.
As far as styling, it looks like you need:
1.) A shirt that looks amazing when tucked into pants
2.) Some fancy looking shoes with cool socks or boots
3.) An added detail such as a coat, hat or vest
4.) Cool accessories that bring out your look
Here some different examples of knickerbockers:
Have a good night! ~ Anna