So here's a simple tip. If you're taking a photo of anything with eyes - ANYTHING - whether animal, bird, or human... catch the light in their eyes. Catchlights!
Assuming you know that the first rule of portrait photography is to focus on the eyes, the second (a very CLOSE second) is to get catchlights. Studio photographers angle their lamps to get the best catchlights, and there are even filters which will ADD catchlights if you've not managed to capture them in the original image.
Simple rule. Short blog post. IMPORTANT!
Here are some with and without examples:
Animals (cute meerkats at that) without catchlights in their little eyes, and with:
Birds - from flat-eyed nothingness to mischievous crow:
And this little cutie pie shows how important catchlights are in photos of people - note the catchlights on the lips too. Texture is important!
Without any catchlights...
...and WITH catchlights:
