Cleaning the dust out of my PC w/ compressed air

So I've had my PC for maybe two to three years now, and quite a bit of dust has accumulating on the inside, particular near the fans, due to there being vents on the sides and top of the tower. Anyway, I want to clean it out, so I bought a can of compressed air (the brand is Stoner Gust, btw), but I'm a little worried about doing this because I don't have a lot experience in this area, so I was hoping you guys could answer some questions for me:

1. I've heard that if you tilt the can, it squirts out a liquid, and this can damage your PC if gets on your motherboard or any other sensitive components. If this happens, is there anything I can do, or is my computer just ruined?

2. Would it be a good idea to try tilting the can and spraying it as practice so that I'll get a feel for how much it can be titled without causing any damage, or would this be a bad idea because it might cause the liquid to get on the nozzle and be sprayed onto my computer's components when I hold it upright and spray the air normally?

3. Is it safe to spray everywhere, motherboard included? I was under the impression this was the case, but I just wanted to be sure.

Thanks.

Oh, and if there's anything else you think I should know, I'd appreciate the input. Again, this is my first time doing this, and I really don't want to screw anything up. I can't afford to get a new computer now if I mess this one up.