If the tree / shrub you want to prune is the one in the picture then what you need to do is use pruning saw, start looking at crossed branches that are rubbing together where this can cause diseases to get into the tree causing even further damage down the way, by removing these crossed branches it will open up the centre of the shrub, the shape you are looking for is like a Goblet, open in the middle and allowing air to flow through the whole tree / shrub, then you can reduce the hight as you will be able to see better exactly what branches need shortened, remember there is nothing worse than having to look at a tree/ shrub that has been hacked to bits without thinking what the end result will look like.
Tree's of differing types have a different appearance and growing habits so they require different pruning / branching. a picture book of tree's will give an idea of shape to go for.
Your very welcome, make sure as you take / make cuts, step back and look all around the tree so you know when to stop or where to prune next. It's not rocket science David, just slow and easy, remember how long it will be to regrow bit's you should have saved ha, ha, ha.
Best regards and good luck. WeeNel.