Love your background Liz it's excellent! Much better than mine, I don't even bother with realistic backgrounds with my pastel, hence why when I finish my last 3 commissions I have at the moment I'm going to spend a couple of months on my own work doing people and backgrounds for a while!
Now onto your drawing...
What type of paper are you using? The paper type can affect how you are able to blend your pastels.
You chose a tricky one for your first pastel drawing! I still struggle with bays still, chestnuts are the easiest to do in pastel colour wise.
You can probably see in your drawing, that you have alot of white patches coming through where the pastel is not covering? This will make your drawing look flat and a bit lifeless when you finish. To bring th horse out of the page, you will need to put a few 'base coats' before you start adding detail. Once you start to use pastel more often, you will work out what colours are best for a certain photograph, but for this one, I would have put a reasonably deep blue for around the eyes, muzzle and darker areas, then a deep red for the other bits. From that, layer a little lightish purple/red over the blue, and a darkish orange over the red. This will come through in the finished drawing and make it stand out.
A big mistake people make with pastel is to just draw the colours straight on, so with yours you have just put brown on straight away. You'll struggle to get the coverage and life in the drawing doing that, so as I said above, always lay down a foundation colour to start with that will come through the drawing and make it stand out off the page.
As for blending, what are you using? Some people like to blend pastels, and for backgrounds this can look good (your background looks lovely!) but if you are focussing on a person or animal don't blend! I lay down solid backgrounds until I start to get into the more detailed layers, then draw the hairs in. Not as fiddly as with graphite though, you can draw less hairs and get away with it. Just layer the strokes on top of each other until you get the coverage you want.
With layering lighter colours onto dark ones, you can do the basic fur that has slightly highlighted areas easily enough by layering light onto dark, but be carefull because it can smudge. If you want to get white whites, leave the area blank, and put down a very very light blue, then the white on top ;) One downfall of pastels is how hard it is to get your whites white but blue is what I've found to work best for me!
One more little tip I've learnt is to use charcoal pencils for alot of the darker areas, they give you alot finer detail than black pastel and you can control the intensity of the colour more. Also, a set of pastel pencils would be a worthwhile investment as you can work on the eyes and such with more precision- it's a bugger trying to get detail in the eyes once your pastel sticks have worn down a bit!!!!
Good luck and looking good so far, if you start off this good a few more drawings later and you'll be fantastic!!