Well the answer to your question depends on how tall the roses are and what type of rose you have. Lets say for example you have a old woody bush rose that is quite tall and looks a mess. The best thing you can do to rejuvinate the old woody rose bush is to get a saw and cut it back hard to a foot from the ground this will encourage very strong new growth to start and will give you a healthy happy rose bush. For pruning climbing roses the answer is different. If you have a climbing rose then you should have trained the mainstems into or onto yout climbing structure. In the spring new shoots will apear from those branches and those are your flowering stems. Once they have flowered it is important to cut them back to about 4 to 5 inches from the main stem above a out facing bud. These stems will be your flowering stems for next year. All climbing roses flower best of the previous years growth. With all rose pruning it is good to look for diseased and dead wood and remove that at the same time. Also with bush roses the theory is the harder you prune back the bush rose the stronger it will grow back. Hope that helps 
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