The only way is up
The best way to train for cross-country is to run off-road whenever possible. Hill running will strengthen your legs, so find an undulating route and work hard up the hills, lifting your knees and working your arms. Alternatively, find a moderate hill to run up hard for about a minute, with a jog-back recovery. Start with six to eight repetitions, building to 12, but don't go so fast that you're crawling by the end. Concentrate on maintaining good running form from the first to the last effort.
The ability to vary pace is very useful in off-road races, when gateways or narrow paths can slow you down. If you spot an obstacle in a race, accelerate through the field so that you reach it before a queue forms. With this in mind, vary your speed while out training by using 'fartlek' sessions, in which you incorporate changes of pace within a continuous run. Fartlek is Swedish for 'speed play' and is based on a form of interval training. Use the countryside to guide you. For example, after warming up you may decide to stride out around the edge of a field, with an easy run through the next field, followed by a series of quick bursts from tree to tree, and so on.
Hills can make or break your race, depending on how you deal with them. On steep down-hills many runners put the brakes on, but it's easier and much faster to stretch out and let gravity dictate your pace. Simply lean forward, lift your elbows out to the side for balance and off you go. You'll find that not only are you travelling faster than more cautious souls, you're also giving yourself a breather, and at the bottom you'll have momentum to keep going. However, this 'free-wheeling' is best done with confidence so practise running downhill when you're out training, starting with friendly slopes and moving on to steeper, uneven hills when you're ready.