Diversity of poses, preparation of the couple involved, and a better location all could of helped the shoot out significantly.
The best advice is learn how to pose people a bit more naturally, or at least learn how to get them interacting with each other in a pleasing way. Also try to convey to them precisely what you want them wearing, especially if they are not paying you to do this the least they could do is wear something a bit more pleasing. It isn't bad, just all blue. Finally the location itself is quite drab, the editing you did on top of the photos makes them even darker and a bit more...uninteresting to say the least. Having lots of dark colors, on top of a darker end editing takes away from the little contrast that was available to begin with this photo.
The next time you have a chance like this I'd ask them ahead of time to clear their schedule so you can shoot for a solid hour. Get many positions in a couple of outfits, really focus on the couple looking natural together and not "Oh hey there's a dude with a camera, FAKE SMILE TIME!" Getting the real smiles from people will be the hardest, followed by getting them to look all comfy.