welcome to GoY
If they are shrub/tea roses I do them in March. Prune to the second from the bottom outward facing bud. I have always cut the stem at a slant so water runs off. I think Percy Thrower 'told' me that many years ago.

If they are climbers then I remove unwanted shoots and tie the wanted ones as close to horizontal as possible. This encourages more flowers.

Jock,
The best time for you would be in March, after pruning give them a good feed of Rose fertilisers, that's for Hybrid Tea Roses, Ramblers are best pruned after flowering.

Agree with the timings mentioned, and the feeding advice, but how much you cut off is down to what variety of rose it is, really - vigorous roses, if cut down hard, will respond by becoming huge, whereas small roses may not put on much growth after a severe cutback. That said, lots of people simply cut them all down near the base and hope for the best. General advice is to always remove criss crossing and damaged branches first, then any which are growing into the centre of the bush, then reduce the height of what's left back to an outward facing bud.

I ordered the book, The Rose Expert book by Dr D G Hessayon from Amazon the other day, arrived today, brilliant book and its the new edition. £1.50 including postage, bargain, lists all the varieties and routine care instructions, wonderful.

I'd recommend the book Dawn mentions above - might be better to get an up to date edition though, because it'll have newer varieties of roses as well as the old ones. Tells you which prune group they belong to as well, so you know how much to cut off and you might be able to identify your own roses from it if you don't know what they are.

When I was in England I always pruned my roses in November. I think a great deal is made of the mystery of rose pruning. I believe that the best way is to try different ways and see what works in your graden. Always cut at a slight slant above a outward facing shoot but don't make the cut to steep.
Continuous dead heading during the flowering period will also boost the plants and keep the blooms coming.
If you want to propgate your roses it is very simple. Take a long straight cutting Strip most of the leaves off. Bash ythe bottom end; leave in water over night and then stick it in a rich soil taht hasn't had roses in it before. Works for me! This is best done in November

And I'd add deadhead properly - I've lost count of the number of people who simply snip off the flower heads when they're spent, making a right mess of the bush as new growth arrives. You might be interested to know that the RHS did an experiment a few years back - they pruned correctly a test bed, and in another, they cut them down to about 8 inches with a hedge trimmer - there was no appreciable difference in flowering, but the ones pruned correctly were better shaped (as bushes) during the following season.