I think the biggest things to remember is that "HDR" doesn't make boring pictures good and is only useful in extreme lighting cases.
Another good one to remember is that "a good photographer is not only judged by what he does shoot, but also what he doesn't". The kinds of pictures you take on a cloudy overcast day should be fundamentally different than those taken on a bright sunny day. To try to use the same approach for both lighting conditions will result in suboptimal results.
Each situation has its strengths for example shooting closeups and macro on overcast days is great because the sky is a giant diffuser. Likewise, shots of people don't work well in the bright sun because all the shadows are too harsh. Sweeping panoramas of a dull cloudy sky don't work well, but they work great in the sun, etc.
Your later efforts seem better than the first ones, especially because they have more compelling subject matter. IMO that one with the rocks in the stream is the best one here.
