Pruning Your Roses: Why, How and When (from springvalleyroses.com)

I would not normally regurgitate information, but in this case, I feel this is very good information to know. I used this process myself this year, and my rose bushes are doing much better at this time, than in previous years. For one thing, I did not prune back my bushes last fall, and used these tips to prune them this Spring. There are only 2 of my rose bushes that did not leaf out from old wood. 

So here it is, straight from Spring Valley Roses: 

Why Do I Have to Prune? 
Why prune? Because it gives your rose an attractive shape, and keeps it healthy by removing dead, diseased, overcrowded and insect-infected canes. Don't believe me? Then, let your roses go without pruning for a season or two and you'll see why you should prune. 

When Do I Prune? 
In the early spring while the rose is dormant or when the buds are just starting to swell. If you prune your rose in the fall, the wounds are more open and susceptible to injury from winter cold and wind. And, you may prune more than you need to or not enough and still have to come back and prune in the spring anyway. 

How Do I Prune? 
The approach to take when pruning is to think about how you want your plant to look. It's like giving your rose a haircut. You need to remove canes that are sticking out in a way you find unattractive or are crossing over other canes and preventing healthy, uniform growth. Pruning is also like giving your rose a physical exam. You might find canes that may have died due to winter injury, insect damage or just old age and need to be removed. There really isn't any other time besides pruning that you give your rose a real good "once over" check. It's a good way to get to know your rose and understand how it grows. Pruning is not something to be afraid of. Just like a bad hair cut, a bad pruning job will usually outgrow itself. We all know that you can't learn to ride a bike by reading a book about it -- you have to just do it. So, think about why you want to cut a cane before you cut it, then just trust yourself and go at it. Understand the basic principles and you'll do fine. 

The basic principles:

1. Wear gloves. Forget the fancy $40 varieties and get a pair of welding gloves for about $7 at your local hardware store. 
2. Get yourself a good pair of pruners and keep it sharpened so it makes a clean cut and doesn't smoosh the cane. 
3. Prune in early spring while the rose is still dormant, or when the buds are just beginning to swell. 
4. Prune out dead, diseased, or insect-infested canes. 
5. Prune out canes that cross over and rub against each other. 
6. Make the cut at an angle so water runs off the cane. A flat cut allows water to sit on the wound, encouraging decay. 
7. Make the cut 1/4 inch above a bud that is facing to the outside of the shrub. The new growth will come from that bud and cause the cane to grow out. If you cut above a bud that is facing in, the new growth will grow in. 
8. Cut back shrubs by one-third every 3 years to encourage branching and new, strong growth. 
9. Cut out one-third of the older canes on climbers every other year to encourage new, strong growth. 
10. Always cut out an older cane before you cut out a newer cane, if you have to choose between the two. Older canes usually have a grey or brownish, weathered appearance.

General Maintenance 
Once your roses are established, which usually takes three years, it's a good idea to do some maintenance pruning. Every spring, prune out the dead wood. Dead wood is brown and dry on the inside, so prune until you see green on the inside of the canes. In colder climates, some roses may die back to the "snowline" and you will need to remove the dead tops. If you're not confident about what's dead and what's alive, wait until the rose leafs out. Then you'll know for sure. Other than cleaning out dead wood, most Shrub roses don't need much yearly pruning. However, you may want to minimally prune some roses to control their shape. When you do this, be sure to prune once-blooming roses after they bloom, or you'll have fewer blossoms to enjoy. But, if you want rose hips, don't prune after blooming. You may find that some shrub roses may seem to bloom less after they are about five or six-years old. They may have lots of large canes that just don't seem to bloom like they used to. To remedy this, prune back the top of the plant by one third, and remove some of the largest canes. This will encourage the rose to grow new canes that will produce plenty of blossoms. 

What About Once-blooming Roses? 
Even though once-blooming roses bloom on "old wood" (last year's growth), they still may need some spring pruning before they bloom to remove dead, diseased or insect-infected canes. But, save all your pruning for shaping until after they bloom, or you'll have fewer blossoms to admire. 

Pruning for Training 
Yes, you can train your roses! For example, if you prune out all but about five to seven strong canes on a climbing rose, all the energy will go into those few canes and they'll grow taller than an unpruned climber. Climbers are usually the ones that need the most training. On a trellis, train the canes to grow at an angle, rather than straight up. This results in more blossoms all along the canes rather than just at the top. Prune back side branches so only about four buds remain. Otherwise, climbers can quickly turn into thickets that you wouldn't want to trip and fall into (you'd be stuck for awhile). 

End Results 
When you're done pruning, your rose should have a well-balanced appearance, with healthy young canes. If you have the time, it's a good idea to seal the cut wounds with Vaseline or Elmer's glue to keep out insects, such as borers, looking for a nice place to lay some eggs.