Smoking in moderation is not a sin at all (CCC 2290). Smoking can be excessive, but culpability may be mitigated by addiction. I recommend talking to your confessor to assess your personal culpability and to get his recommendation for how often you should confess. The Church urges Catholics to confess their venial sins because the grace received in confession can help heal them and strengthen them against future temptation (CCC 1458). I also recommend praying for the intercession of Dorothy Day, the American Catholic social activist, whose cause for canonization is under investigation. Day was a heavy smoker for much of her life.