Try to dress on the same level of “dressiness”.
Meaning try to be cohesive: smart but casual OR dressed up a bit, like for a date. You don’t need to match colors unless you just want to. Keep in mind that if it isn’t wet, we may sit on the ground.
Wear shoes that are comfy for walking (or bring some). If you go the more casual route, sporty sneakers are fun but usually ordinary running shoes or ultra white sneakers don’t photograph as well.
High heels are great, as long as this is normal for you.
Sometimes women want to wear high heels for the photos and it’s their first time! Needless to say it’s not always comfy.
Regarding the colors, keep it simple.
Rich jewel tones, bright colors, or dark colors look best. So stay away from overly busy patterns, or an entire outfit in a pastel. You can even put your outfits together and see for yourself if they work or clash.
In terms of outerwear, the same applies. On cool days, or just for styling, I like layers: scarfs, hats, and all sorts of accessories. Plus if it’s chilly out, you can remove your jackets for some of the images without being cold.