Can someone please explain to me why artillery will fire on a hill one and not the next. sometimes i have to click 10 or 12 times before it fires.

maybe you dont have it pointed at a surface?

The binoculars can be decieving. At first I aimed where the horizontal and verticle lines crossed, because I was expecting crosshairs. Well, half the time I couldn't get arty called in. Until I realized that you are supposed to use the half circle in the center of the scree to aim. It made sense after I thought about it, but it wasn't obvious. I'm guessing this may be your problem. Also, if there is a tree branch in the way of where you are calling arty, it usually won't work, but thats only happened to me a couple of times.

And also make sure that your artillery is ready. I know I've gotten pissed a few times when my arty won't come, only to realize that I hadn't waited long enough for it to ready up.