Answer: If this rose has been growing there for ages, a few pruning mistakes won't kill it, I promise! But timing is important. In the north, roses should be pruned in late winter/early spring, before it starts active growth. It sounds like your rose hasn't had this kind of attention in a while, so there's likely some dead and spindly growth to remove. You can remove the dead stuff this fall, just to clean it up before winter, and to make the spring pruning more manageable.
In the spring, take a look at the bare branches of the rose to get an idea of its natural form. Let this form guide you; remove the spindly weak growth first, and next prune out really crowded shoots. Open the center of the rose up, and more light will get to the center of the plant, and perhaps it will bloom lower on the plant as a result.
It's good to step back from the work frequently to get a look at the whole rose, and make sure you're pruning to keep a balanced look to the plant. Once this basic pruning is taken care of, you may feel confident to train the shape more to your liking...but maybe that should wait til next year, when you're more confident of your pruning skills. Enjoy!
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