Rugby.gr

I was browsing the IRB site when I saw this nice article.

The IRB’s Game Analysis Centre, headed by former referee Corris Thomas, has just completed a full review of the 2006 RBS Six Nations Championship. The report analyses the trends from every match, and gives an in depth insight into how France won the championship.
The report showed that possession is not a prerequirement to possession. Despite having on average three minutes less possession per game than England, France were the most effective team in converting possession into points. France scored a try for every 5 minutes in possession, Triple Crown winners Ireland scored a try for every 8 minutes possession, England 9 minutes, Wales (2005 Grand Slam Champions) required just under 10 minutes to score a try, Italy 15 minutes while Scotland scored a try for 17.5 minutes in possession. France was also the second most effective team in preventing opponents from converting possession into tries (on average it took sides 21 minutes of possession to score against France). Scotland, with an improved defence, topped the standings, while Wales propped up the table with opponents requiring just under 6 minutes of possession to score a try.

Basically you need a good attack to make the difference each time you put your hand on the ball and a good defence to get that ball.