Hi EzyStyles, if you are just visually observing planets and DSOs I wouldn't be terribly concerned about a bit of dust on your primary mirror - the decrease in contrast caused by a little dust is negligible compared to other factors such as poor collimation, insufficient scope cool down, or bad seeing.
If you are doing hi-res planetary imaging then you need to have everything perfect and cleaning your mirror every 3 months is just part of the fun and games
If you do want to clean your mirror, I don't think a hairdryer is the way to do it - blowing tiny abrasive particles across the surface of your mirror may cause fine scratches. Follow the link that iceman has provided to learn how to clean your mirror properly.
OK, just saw your last post - good luck with the washing. Yes, do use distilled water so there is no residue after the water dries.