Chris O'Callaghan - qualified mountain bike leader (mbl). Chris has been mountain biking since 1999 with qualifications in all outdoor education since 1992.
Chris and Liam Sheehy run Trailriders Bike Rental in Ballyhoura Forest (trailriders.ie) with a fleet of 40 bikes in Irelands largest trail network (offering bike hire, kids training camps and adult lessons from trailriding to racing).

Below for Madforsport.com, Chris goes through essential information/ what you should know about Mountain Biking:

1. Always pick and buy a bike from a proper bike shop as there is a lot of non experienced bike shops out there that will sell you anything (pop to your local trail head and ask any of the bikers)
2. Hardtails are always the best option to learn the basics of moutainbiking as it’s a cheaper option but also less weight to be carrying around (remember to pick the right tyre choice as too big a tyre means more rotational weight)
3. Always wear a helmet and dress appropriately with jackets and footwear. I normally suggest to treat it like a 3 hr hill walk with clothing/food as you are going into the mountains.
4. Make sure that the mountain is safe for biking. I would recommend to use the Coillte Biking Trails which can be found on the Coillte and Madforsport.com websites
5. The rule of thumb on the trails with the mix of abilities is that the slower racer has the right to go at his/ her own pace but when appropriate should pull over to let off the faster racers
6. The best way to get started really is a local club, most mountain biking clubs have a full selection of disciplines adventure racing/x country to downhill (even downhill in Europe).
7. At the start it is a good idea to take a course in mountain biking to learn the basic techniques. Ensure that the course provider that you go to has qualified mountain bike leaders. There is a list of course providers on madforsport.com along with an overview of the courses
8. The mountain biking course provider will go through mountain biking etiquette and safety tips