Tips on couple portraits?

I plan on taking a few pictures of my mother and her partner tomorrow and want them to be as nice as possible. My camera is a Nikon D3000 and we're going to take the photos in the park. What are some good tips to remember?

Go early in the morning, like 8 or so. The natural light is beautiful around that time, and your subjects won't squint because of the sun either. Everyone wins.
Also, have them wear matching colors (like black or white) or even two corresponding colors (like black and white together!) to make the picture aesthetically pleasing to the eye and look simply beautiful. Try not to wear something with heavy designs or graphics because that will distract from the photo.
Try to take more candid shots rather than just posed stiff shots. Take photos of them being themselves and being natural together. You can still take the posed shots, but try to get them acting normally also. Those pictures are the best ones and show true character.