Hi Terri,
I appreciate that the shorelines of lakes or beaches may not always parallel to the camera, but where you can, I would suggest levelling shots where this looks better, as I think it might in some of these - although they're not off by much.
On the two island shots;
The exposures look reasonable as processed, although I do note (from histogram) the blue channel has blown on both, losing you some saturation in the sky.
From water level, especially with a land mass behind, I think it is difficult to separate the island from the background, aerial shots always win to my mind, not that that helps much beyond acknowledging the difficulties faced here. Sometimes mist or spray can help with separation, but you're obviously reliant on suitable weather for that - and not the sort that would be welcomed here, I'm sure
![Big Grin](https://cdn.cambridgeincolour.com/forums/images/smilies2/biggrin.png)
Another distraction are the boats; they're bright, so attract the viewer's eye away from the subject.
You may have noticed I haven't mentioned the rule of thirds yet, that's deliberate; I'd consider the things I have mentioned more important than applying the rule of thirds rigorously. Put another way - and this does not apply to you because I appreciate you are using these for cropping practice - if a photo doesn't stand on it's own merits, the rule of thirds isn't going to save it.
With these two, I get the impression you are thinking that the horizon should go on a third, the choice being; which one? The result being the other two thirds will be filled with water or sky, choose whichever is more interesting.
I might have tackled these by getting closer and shooting at a wider angle than the 20mm used on your Nikon D5100. This could give one third each water and sky, with the middle third filled with trees - or maybe that's no better - anyone else got any ideas or experience to share with Terri and I?
Hope that helps,