1. If you want to take advantage of those repeating lines and columns in the background, use a telephoto focal length to create more of a 'tunnel' effect. If you took a step to the left the perspective of the 'tunnel' would lead your eyes right to them.
The knees are a really awkward place to crop people at.
Engage his hands. Have him hold her waist or something.
Get them to snuggle up closer in; they look a bit too separated.
2. There is some crazy background distractions going on. Get far away and use a high focal length like 200mm. This is to minimize the amount of background that gets into the shot. If you took this shot at 200mm but kept the people the exact same size in the frame as your shot, you probably wouldn't even see the huge building in the background, nor the weird stump on the right, and it would mostly get blurred out because none of these items (except the pathway) are really contributing to the shot.
The contrast seems a bit low. Try playing around with channel mixing. It looks like it might be a straight desaturation?
3. This type of shot seems to be popular. But you're not close enough to the ring. Get really close to it in order to make that ring really in-your-face for your shot. Then there will be NO mistake as to what you are trying to showcase. Although the people are blurred, it would be more interesting if they were both engaging each other, rather than her looking at her ring. Since your focusing distance would be much closer, it would also improve the bokeh on the people, which is rather ugly in it's current state. The exposure on the people is also rather low, even though the exposure on the ring is good. Either flash to balance them, find a natural light angle that will light both them and the ring, or bring up the exposure on them in post.
4. it is nice... but again, get closer to that ring for a stronger effect. Use a lower focal length. A lot of these (if not all) look like a 50mm focal length if I were to guess.
5. almost worked. The composition is great and the exposure balance between people/background looks nice to me. But the posing/positioning is awkward. They need to be much closer in together. Engage her hands... put her hands around his neck or something. If she wants to put a foot on the wall, get her to use her other foot so it doesn't obstruct him.
6. the white balance looks off. She looks like she is in the middle of a blink. Take at least a couple shots of the same pose just in case of blinks. Have her move her head forward towards him more and lean in a bit closer. A slight change in torso and neck angle will do wonders for her chin/neck.
There is a lightpole growing out of his head.
There is so much space around them in the shot. It could have been nice if you got it in focus to show them in their environment, but you chose to blur the living snot out of it so you cannot really enjoy the beauty of the garden. If you want to show the garden, let us see it. If you wanna blur everything in the background out, then fill the frame up with the people more. People surrounded in tons of blur can work in some cases, but it doesn't in this case.
Overall it's a good start. Keep practicing and you'll get the hang of it in no time. Thanks for sharing!