Developing your body's ability to use oxygen to convert fat and carbohydrate into energy to turn your pedals should be where everyone puts their focus initially. The newer you are to mountain biking the more emphasis you should put on this aspect of your training. In saying that seasoned campaigners can benefit greatly from a focused training block revisiting the development of their aerobic endurance if they have been spending a large amount of time performing higher intensity training loads.
How to do it: Get out and ride at a steady 'conversation' pace clocking up some time in the saddle and banking some miles. Most reading this article will be familiar with this type of training and most will normally do this training at an intensity which is higher than this Zone 2 conversation pace leaving them tired and unable to train at higher intensities in their other important training sessions. So with this in mind keep a check on your training intensity, harder is not always better.
2) Body maintenance
Once you have got a good aerobic base under your belt I believe the second most important place you can put your training focus in on your body maintenance. As you start to push your body harder in training your body will start to push back against you. This is when you will start to develop aches and pains that can seriously affect your training and racing. The good news is that a little time spent on body maintenance goes a long away and makes a big difference.
With approximately 1200 m of climbing in the Motatapu course it is important that you can not only keep your pedals turning for the full 47 km but you are able to generate the force required to climb the hills at a speed that keeps your bike rolling upwards and not having to get off and walk like so many others. Being able to ride past a line of people pushing their bikes is a great way to avoid hold ups and slice minutes off your race time.
How to do it: In short hit the hills. Long hills, short hills, steep hills, gradual hills, the more the better. As a good rule of thumb if you gravitate to climbing seated then work on getting out of your saddle more while climbing. Likewise if you prefer to mash those pedals out of the saddle then you can probably benefit from spending some more time climbing seated.
4) Technical skills
While the Motatapu is not an overly technical course in the scheme of things, having good technical bike handling skills can allow you to maintain higher downhill speed on the rough descents to make the most the free gravity assisted speed. If you can develop your riding skills on single track then when you hit the open 4wd tracks you are going to be able to rip it up.
How to do it: Spend time on single track and rough terrain that challenges your bike handling skills. Riding with other riders who have better skills than you is a great way to push your limits and see firsthand what can be done or if you want to step things up another level one on one or group coaching options can be money well spent.
5) Anaerobic threshold
If you have addressed the above 4 points then you are ready to start putting your time and effort into developing your anaerobic threshold which will improve your ability to sustain a higher race speed. If you have not already invested your time into the above aspects of your performance and just jump in to your anaerobic threshold development the extent of your gains will be limited as you will not have the solid base to build off.
How to do it: This type of training is best done in the form of interval training where you dial up the intensity and ride at a 'hard' intensity and have periods of easier riding between these harder efforts. If you are new to this type of training start by trying 4x4 min intervals at a hard intensity with 2 min of easy riding between these. Add in a steady warm up and warm down and you have got a great way to get some race fitness under your belt in a short space of time.