Looks like you're off to a good start...
Since you asked - but please take this only as one opinion. I'm sure others will chime in as well.
#1 and #2 fall into the same response... Shooting that close, even at f/8 at 55mm is going to give a fairly thin DOF. With flower type shots (at least for me) you have to carefully look at what will be in focus and what will be out of focus. In these cases, the water drop was I believe your focal point and you'll notice the leaf coming at you is now out of focus, but on either side it IS in focus because it's a different distance. ie: the focal area is now split in two places. That draws away from your eye. So try a really shallow DOF next time, like f/1.4 or 2.0 and see what happens. That will make the focal point be THE focal point and everything else will be a blur. Conversely, shoot f/16 or f/22 and bring the whole flower out.
#3 more closely aligns with what I mentioned above. I like it. Maybe next time try to put some context with the shot such as part of the stem of the rose. Believe it or not, using the flash on stuff like this during full daylight really can make a flower or image "pop" with color.
4/5/6 I have to ask myself, "what are you trying to tell me"? #4 looks like the camera did a nice job of exposure for what appears to be fairly bright sunshine. #5 has the tree coming out of the handlebars so maybe next time really look at what the image will be, and ask yourself "what do I want to tell". In the future, for #6 type shots, decide if you want to be in the image or not and focus on that. If you want in it, then make that a significant part of the shot, otherwise try to keep yourself out of it.
I'm glad to see how well that 5100 does in matrix mode on bright conditions and you most probably having some shadows. I think you're probably going to like that body and post 'em up as you create them! (we love looking at shots in this little part of TWT)
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