just got my first DSLR camera, very new and could use some help!
 

Okay, so I got a Nikon D5200. My first slr camera from "point and shoots". I got it only two days ago and have been snapping pictures using my pets as test subjects. What I would like to do more with the camera is practice selective focus. Would anyone be able to help me and give me some advice?

Short of a photography course, your best bet is (IMO) getting a good book. I got one from the For Dummies series that I was finding pretty helpful in sorting out all the functions. You may have some luck with youtube instructionals; but when I went that route, I found them tedious and lacking.

Depth Of Field is going to be your friend when trying to photograph reptiles, especially long ones like snakes. It's amazing what you can do by manipulating aperture size.
You also want to concentrate on shutter speeds and exposure values to get images that will be very pleasing to the eye. Your manual should have sections dedicated to the explanation and use of A and S modes.
Lastly, do yourself a favor and familiarize yourself with focus points. When the eyes are in focus the chances of a more satisfactory photo are greatly improved.
As an example, notice the depth of field causes the rear portion of this Garter Snake to be somewhat blurry, however the crisp focus on the eye makes it a pleasing photo altogether.
http://i51.photobucket.com/albums/f3...ps50f8b03d.jpg

Thank you for the advice, that's the kind of focus I want to learn with this camera and macro of course. Basically I'm looking to take photos like the one I attached

Dial your aperture setting way down and you should be able to recreate that effect (or better) easily.

It's when you need a lot of depth of field that things start getting tricky.

Ok I'm going to try that and see how my photos come out thanks!

Exactly.
After a little practice you'll find it very easy to do.
http://i51.photobucket.com/albums/f3...ps11cac6e2.jpg