Rolls are a classic Irish ornament. They take some finger strength and technique on a guitar, but they're a good exercise, and they'll actually give you a technique you can use in real playing.

To do rolls - play 1st finger on 2nd fret, hammer on with 3rd finger at 4th fret, pull-off to 2nd fret, pull-off to open string, and hammer-on again to 2nd fret. Then try that with 2nd and 4th fingers, and 1st and 2nd fingers, and 3rd and 4th fingers. Having your left hand in a proper classical position (rotated so that your hand is completely parallel to the neck instead of at an angle - pull your elbow into your side for this) helps for technique. This practise also ensures you're playing with the tips of your fingers, instead of cheating by using the pads, because you can't do hammer-ons with the pads of your fingers.

Once you've got that, try rolls somewhere up the guitar neck, playing 2nd/3rd finger, hammer-on to 4th finger, pull-off to 2nd/3rd, pull-off to 1st finger, hammer-on again to 2nd/3rd finger.

Another thing with finger dexterity is how far you can reach. A great exercise my guitar teacher got me doing is playing the bassline from "Every step you take" - this needs your fingers to go over quite some distance. Start with a capo around fret 5 or fret 7 to make it easier, and then move the capo down (giving a bigger distance between frets) as your fingers get better.

Graham.