Which way you turn the barrel adjuster depends on the specific problem you're having with your cable tension. Almost all rear derailleurs are "high normal," meaning the spring action of the derailluer wants to pull the derailleur outward, to the smaller cogs (higher gears, hence the term "high normal"). Front derailleurs are opposite of this, the spring action pulls the derailleur inward, to the smaller ring(s), lower gears (front derailluers are "low normal"). So to determine if the cable on, say, the rear derailleur needs to be tightened or loosened, you have to determine if the derailluer is out of adjustment in such a way that it's trying to pull a little too hard outward or inward. If you're in, say, the third cog, and you're hearing a little clicking back there and you determine that the derailluer is pulling the chain a little to the inside as it rides on this cog (trying to pull the chain to a larger cog, lower gear), then you've got too much cable tension and the barrel adjuster needs to be turned clockwise, which will, affectively, loosen the cable tension. If the rear derailleur is doing the opposite of this, trying to pull the chain outward, to a smaller cog (higher gear), then you don't have enough cable tension to counteract the derailleur's spring, and the barrel adjuster should be turned counterclockwise, to affectively tighten the cable tension. Front derailleur adjustments with the barrel adjuster work oppositely, because they're "low normal," but the principles are the same, and the cable is still affectively tightened by turning the barrel adjuster counterclockwise, loosened by turning clockwise. Good luck-