Engagement portraits are a fun way to capture your personalities and the story of your love. These sessions should be relaxed and fun. Choose locations with significance to you; the place you had your first date, a local park to reflect your love of the outdoors. If you cannot decide on a location, ask your photographer what they would suggest for you.
It's always fun to throw in a mix of clothing, formal and casual outfits. Solid colors and coordinating (not matching) outfits are ideal choices. Solid colors allow the focus to be on you instead of the pattern of your clothes and coordinating clothes really help to tie you together in the pictures. Matching outfits tend to look too unnatural; not to say you can't both wear white tops with jeans but the subtle variations between your clothes will set you apart enough and add interest to the photo.
Also engagement sessions are a great way to bond with your photographer before your big day. It is a chance to really get to know each other so you are more comfortable working together.