I've taken a few over the years and generlly find that semi-ripe heel cuttings are the best.

You need to find a good strong shoot around 8" long and pull it off the mother plant so as it leaves a 'Heel' where it's torn away from the main stem.
Next trim off the very tip of the heel so it's squarer and less ragged at the end.
Remove around 2/3 of the leaves up the stem leaving only the very few at the top, then dip into some hormone rooting powder and place into a 3" pot to around 3-4" inches deep.
The pot should be filled with a very sandy, loamy mix with a little peat chucked in for good measure.
A heated propagator is really a good idea when it comes to semi-ripes as it helps the roots to form quicker, but if you haven't got one, the put the pots of cutting into a tray and make a little 'tent' out of polyethene to help retain humidity and warmth.
Make sure that the cuttings are then placed somewhere out of full sun but with good light and water them just enough to keep them on the wet side of moist.
Then after about 3-4 weeks they should start to root.

Oh and the time for semi-ripe cuttings is from very late july until early september.

Hope this helps :-)