How to achieve quality pictures on tumblr?

Those who use tumblr, you know what I'm talking about. Those quality pictures that are really clear and the colors just pop. They look really nice. I have a Nikon D3100 and most people use Canons but I don't think that's what gets them those pictures. What do they do to edit them or how the shoot it? Help?
Here's some examples:

I've been told my pictures are nice… I don't edit them at all. I always think photos look best when they are in focus and have depth. A clear subject is the goal. It needs to have color or some kind of detail that stands out.
These are some of my photos:
http://jdcountrycutie.tumblr.com/

The same way you achieve "quality" images anytime, by understanding your camera. Classes, reading, reading the manual and experience all help. The Island image was lifted from another source, as I suspect the first was. The third won't work for me.

With Tumblr, you can upload your photos to a potentially large audience and make them active links for other webpages. You can submit your photos to Tumblr by visiting a special webpage and supplying the same basic information that most other photo submission sites require. Once you have submitted your image to Tumblr, it can be viewed by millions either on their computers or their mobile devices. Submitting your files to Tumblr is a straightforward process.

1. Open your Web browser and type "http://impostingon.tumblr.com/submit/ph… Into the address bar. Press "Enter" to be taken to Tumblr's photo submission site.

2. Click the gray "Choose File" button beneath and to the left of the "Submit a Photo" header.

3. Locate the photo that you would like to submit to Tumblr with the Windows Explorer window that opens. Double-click the image file to insert it into the submission form.

4. Enter a caption for your photo in the space provided if you so desire.

5. Click the white checkbox to the left of "I accept the Terms of Submission" entry.

6. Enter your email and name in the space provided.

7.Click the large gray "Submit" button to send your photo to Tumblr.