Choosing the right outfit is hard on the simpilist of days let alone trying to style and coordinate for your engagement pictures! I get it, it can be stressful. I am by no means a clothing/style expert but hopefully my thoughts can help ease the stress for you a little.
Where to start: I always start choosing an outfit by first deciding how dressy or casual I want to be. For your engagements there are a few traditional options you can do. You can go all out and be dressy for the whole shoot with a dress, heels and a suit for the groom to be. You can do half the session dressed up and then switch to a business casual or casual or you can just do casual. It's really up to you but once you decide this it makes putting together outfits a lot easier because you have some guidelines to start with.
Color pallet: Choose colors that compliment you and your fiance's skin tones first and then choose coordinating (not matching) colors so you don't look too matchy-matchy. Try to stay away from blacks or bright whites because they can look harsh in photos. I suggest sticking with soft neutrals like blues, creams, pinks and the like.
Patterns & textures: I love when client's wear textures and patterns like lace, florals and stripes to a shoot, it adds personality and depth to photos. Just make sure your patterns don't clash and that they are not the focal point of your outfit because then you run the risk of your clothes competing with you in the photo.
Layering is in (always): Don't be afraid to layer with cardigans, vests or scarves! They can help break up an outfit with pattern and add interest to your outfit.
Mind your accessories: My opinion on jewelry is if it's too trendy it's best to leave it out. Remember those chunky crayola colored big ball necklaces everyone use to wear? Have you seen people's engagement pictures with those? I have and trust me, if your jewelry isn't subtle and it too trendy save it for other pictures. But classic delicate jewelry and hats that you look great in are always a plus.
Last (but not least!): Make sure the outfits you choose do not overshadow you. You will want an outfit you feel beautiful and comfortable in and that compliments you nit takes over the picture.