Life drawing is indeed very important and you should do it as often as you can. (This helps you understanding and drawing movements and shadows, for example)
But as you can't draw mammals every day (I guess), take a look for reference photos photos in the internet.
http://commons.wikimedia.org/wiki/Main_Page <- this site contains a lot of photos that are under a creative commons contribution (I hope it's correct to write it like that, sorry for my bad English.).
Some hints in general are:
- look at the animal you want to draw in different angles to get a better understanding of its anatomy (it's just simple studying)
- make really rough sketches (such that only take a few seconds or a few minutes) of that animal with the help of your reference photos, try not to use your eraser
- when you think you understood the forms of the animals you want to draw you can finally start to do a rough draft of that animal that will be the base for your final drawing
- even if you understand the forms of your animal, keep on using references for some details such as fur length and direction, as well as the basics of shading
- take your rough draft and fill in the details, take your time, there's no need to hurry
- practice
- practice
- practice even more (as often as possible if you want to improve really fast)
- most importantly: never give up
There are countless techniques for drawing animals, just try to look for one that suits you and your style best (there are countless tutorials on DA).
Just a few examples:
http://panhesekielshiroi.deviantart.com/art/Losing-my-reflection-85011278 <- I did this one about one year ago without any photos for reference ... As you can see, it's not very good and doesn't even look like a snow leopard (it's slightly anthropomorphised).
http://panhesekielshiroi.deviantart.com/art/Grey-autumn-106509917 <- I did this one last December. It's not perfect but it looks way better than the snow leopard portrait. I used a photo a friend of mine took as reference (I got his permission) and anthropomorphised it slightly.
As for wild life illustrations I have only one picture to show:
http://panhesekielshiroi.deviantart.com/art/Alopex-lagopus-105428649 <- Again, anything but perfect. But still not thaaaat bad. I used no reference photos for this one, because I was studying the specific characteristics of arctic foxes before (oh well, I guess I would have done a better job if I was using references).
I hope that my long and boring text is able to help you a little bit. Good luck and feel free to ask more questions if there's anything you don't understand.