You're getting some very good advice here and I just want to add a couple of things...
What madweasel said about learning composition is right on the nose. Cameras now a days are amazing devices but the single thing that will improve your photography more than anything else is understanding the elements of composition. A "good" photographer can take amazing pictures with even the simplest point & shoot camera and that's simply because they know how to compose an image. As I've said so many times, it's not the camera, it's the person using it.
I was also like to make a comment in regards to tripods as well. -If- you can afford it, then by all means get the Manfrotto or something similar...I'm sure it will last you a life time. However as Madweasel also hinted at, regardless of brand make sure you get yourself something that is reasonably light weight as well. Even if you spend $400 on a rock solid tripod, it's not going to do you any good if it's sooooo heavy that it spends the entire day in the trunk of your car. With that said, since your just starting out I would honestly suggest getting a cheaper one than the Manfrotto's until you have a better understanding of what you're actually going to need. Personally I've been shooting for over 20 years and my favorite tripod is actually a $20 "department store special"...it's light, reasonably stable and does the job -very- well for my needs. In the mean time also remember that other things can be used to stabilize your camera as well...tables, fence posts, rocks, hand rails, the tops of trash cans, etc., etc.. Any flat, stable surface will usually do in a pinch.
Now as far as your shots go, they're reasonably sharp, the colors look pretty good and I'd say your off to a pretty good start. The repost of the frog with him facing you is by far the best. I think I'd crop that one in just a bit, keeping the rule of thirds in mind and put the frog in the upper right hand third "sweet spot". Maybe punch up the saturation and contrast just a bit and you'll have a nice print.
Good Luck!
Jim
"It is horrifying that we have to fight our own government to save the environment. " - Ansel Adams
Walczak Photography - www.walczakphoto.izfree.com
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