The main challenge is the one of movement - you can't ask a dog or a cat to hold a pose for half an hour or even 10 minutes. Even sleeping animals tend to move around quite a lot to change position for comfort. This means that it is no use being tentative. You have to try to capture the essence of the body position and character of what you are drawing very rapidly. You can always take advantage and work it up into a more detailed drawing if the animal unexpectedly keeps still but is best to assume when you start that there is a very limited window of opportunity. It is much more difficult to capture an animal's vitality when drawing from a photo.
Which media did you enjoy using most and which did you feel were best for the subject matter and why?
I enjoyed using biro for the quick sketches of cats. You can draw rapidly and confidently with this without worrying about damaging the nib of the pen.
I also really enjoyed using the oil pastels for the fish. I thought these worked really well for the reflective surface of the scales as I was able to use opaque white pastel on a dark background for the highlight and multiple colours together for the reflections in the scales.
As an aside - for quick sketches at work I found a drawing app on my I-pad that was quite useful. This meant that I could draw with confidence without wasting reams of paper when drawings weren't coming out well.
Where can you go to draw more animals?
I have a lot of opportunity for drawing animals where I live. Most of our neighbours have at least one pig and lots of chickens. There's a dairy farm up the road and a buffalo farm a few minutes' drive away (for buffalo mozzarella). I had a lot more opportunities for drawing interesting animals at work (particularly wildlife casualties) than I actually had time for drawing. I've taken photos but am wary of drawing from the photos.
I could go to a wildlife park or zoo to draw. I also really liked the fish exercise so perhaps I should go to the aquarium? When I win the lottery I'll go to the Galapagos islands and take my son on Safari in Africa!