Keep your hooklength fairly long. Both Lee Swords and myself favour long fluorocarbon "Incognito" hook lengths. Sometimes I use hooklengths over 1 metre in length.
I have used the 9lb stuff and the 12 lb stuff in the past. It depends where I have been fishing. There are very rocky places on the Trent where a hooked barbel will head for. If you don't stop them you will then feel that horrid grating on your line to be followed by a breakage.
I am sure a fluorocarbon hooklength is of advantage in daylight conditions and I am fairly well convinced that it's weight also helps.
Remember that over the years, fluorocarbon has recieved a bad reputation it doesn't deserve, mainly because people have misused it, tied the wrong knots, but most of all there has been some awful fluorocarbons around. Good fluorocarbon will help you catch fish; poor fluorocarbon will not.