Once you join the officer ranks, you’ll receive notifications upon logon about your skill level.
Skill level goes from 0 to 200. If you have a skill level of 200 you’re supposedly a top player.
The algorithm with which skill level is calculated is a mystery. Most agree that it takes into account the SPM (Score Per Minute), KDR (Kill/Death Ratio) amongst other metrics and factors.
It has also been reported that if you don’t play for a number of days the skill level drops to 0 (…).
UPDATE: The skill level does not increase if you’re off for a few days.
In any case, you shouldn’t worry too much about your skill level because it doesn’t necessarily reflect your skills and how well you play. For instance, it is weird that DICE chose to partly base the skill level algorithm upon the KDR, since BFBC2 has been built in order to discourage players who are only interested for the kills, and this is one of the reasons why I/we think the game pwns Modern Warfare 2!