From this post at Scientific American:
Fowler and Aksnes (2007) did another research on the Norwegian database, but this time it was author rather than publication oriented. The percentage of author self-citation was rather low – 11% – but every self-citation yield, on average, 3.65 citations from others in 10 years. Fowler and Aksnes concluded that “self-citation advertises not only the article in question, but the authors in question.”
So yeah. Cite your own papers. Liberally.
Fowler, J. H., & Aksnes, D. W. (2007). Does self-citation pay? Scientometrics, 72 (3), 427-437 DOI: 10.1007/s11192-007-1777-2