How to take better pictures?

I love taking pictures of animals, nature, city, flowers, and just about anything but, it seems like I'm not any good. I'd like to be able to take really good "natural" pictures like profesional photographers. Any advice? Here's some of my shots…

Nikon D5100

Many people will suggest you take a photography course, and yes, that is a great way to learn to take better pictures. However, there are a few things you can do before (or instead) such courses.
Your camera has only one eye with which to capture the image; whenever you are considering taking a picture of something / anything, close one eye so that you see the subject in only 2 dimensions. Now concentrate solely on what it is that you want in your picture. That is what should fill most of your viewing screen.
There are many other tips, but these are 2 of the most often overlooked by people who only take 'snap-shots' instead of great pictures.

Learn to "see".

There are a lot of information you can get online these days… And I know a lot of "self-taught" photographers.

Yes, a basic photography is a great start learning from experts but if you've taken a course before you can ommit this comment.

A group or club can also help to improve your photography by sharing some ideas

but If you don't have many friends that are interested in photography or groups are hard to enter or find maybe a photocontest can help you improve. If you win you get a prize but if you lose it's not a total lost cause you can check the winning photos and study why the judges choose it and you can try it so in a way you learn. If there aren't much contest going on there are site like dpchallenge.com that conducts weekly contest on different themes for free (no prize though only bragging rights.