I have inherited an area of land that has not been cultivated for many years - 25+. It contains a number of holly trees. I say trees because they may well have initially been single stems that have just been allowed to grow naturally without pruning. Some we have removed but I would like to prune and retain some, but they're 12 ft or more high with 9'' circumference and branches trailing 3-4 feet from the trunk. They're heavy with berries at the moment. My question is - how do we prune to enhance growth and provide some shape?