Having spent a fair bit of my rugby career in this position (including, indeed, my most recent attempt), I feel reasonably well qualified to dish out with impunity a multitude of advice on how to play Number Eight but, in order to perhaps gain a little perspective, I feel I should first check out what Wikipedia has to say on the matter...
The modern number eight has the physical strength of a tight forward along with the mobility of other loose forwards. The number eight packs down at the rear of the scrum, controlling the movement of the ball to the scrum-half with his feet. The number 8 is the position where the ball enters the backline from the scrum and, hence, both fly half and inside centre take their role from the number 8 who as the hindmost player in the scrum can elect to pick and run with the ball like a back...They are normally tall and athletic and used as an option to win the ball from the back of the lineout... [and] need to be quick to cover opposition half-backs. A number eight should be a key ball winner in broken play, and occasionally a 'battering ram' at the front of rucks.
Hmmm...perhaps I don't know quite as much about this position as I thought I did. Let's take some of these assertions one by one:
The modern number eight has the physical strength of a tight forward along with the mobility of other loose forwards. Errr...no. In my experience it's usually one or the other. Either you're a great lump of a bloke who would happily play at lock if it wasn't for the fact that you are way too heavy to lift, or you're a flanker who fancies getting his hands on the ball a bit more often but is likely to be out-mauled by an asthmatic kitten.
The number eight packs down at the rear of the scrum, controlling the movement of the ball to the scrum-half with his feet. Well, yes, this is a possibility, but it does assume that the scrum in front of you is rock solid and that your hooker has heeled the ball down the correct channel. In reality the situation usually involves the Number Eight screaming "Ball, ball, ball!" as the scrum shifts into reverse gear and the ball gets stuck under the second rows' feet. When the ball eventually does reach the back the only option is to pick the damned thing up to prevent further carnage, much to the delight of the opposition back row who then pummel you into the ground just after your own second rows have stamped on your feet.
...as the hindmost player in the scrum [the Number Eight] can elect to pick and run with the ball like a back. Now, I'm not sure who actually penned this entry in Wikipedia, but I'd be amazed if they ever actually played rugby. To most forwards running "like a back" is the equivalent of "running like a girly" and, to be fair, if you can actually run like a back then that's usually where you are selected.
They are normally tall and athletic and used as an option to win the ball from the back of the lineout. All fine and dandy but how many hookers can throw to the back of the lineout with even a smidgen of accuracy?
A number eight should be a key ball winner in broken play, and occasionally a 'battering ram' at the front of rucks. Oh is that all? While I'm at it why don't I also score all the team's points and then lick the changing rooms clean?
The crux of the matter is this - if your pack is going forward then Number Eight is just about the most enjoyable position on the field - you're able to control the flow of possession to your backs, get your hands on the ball, run off the back of scrums, stand off rucks and mauls, take short pop passes from your scrum half or generally gallop freely around the paddock acting like a right smartarse prima donna. However, in my experience these occasions are few and far between and, invariably, when your pack is under real pressure, then the opportunity to get your hands on the ball swiftly becomes a curse as all it involves is being mullered by the opposition back row at the back of retreating scrums, being mullered by the opposition back row while attempting to tidy up wildly tapped lineout possession and being mullered by the opposition back row while trying to secure ruck ball yards behind your gain line.
Admittedly there's rarely a dull moment, but my advice is this: Never volunteer to play Number Eight if you want to blend into the background and go unnoticed. That's the blindside's role.
Hope that helps...