The "Norm" for using any compressor, is using the least amout needed to reduce clipping or distortion. You also need to consider other factors, such as, gating, and selecting attack/release time levels, if using it in a manual mode. There is a lot more to it than just selecting a ratio to ensure sound quality is smooth and you don't end up with "pumping" and "breathing." You also need to consider what type of FXs you are using on the vocal. What compressor/gate are you using?

Consider downloading the dbx "Compression 101" primer at http://www.dbxpro.com/ftp_mirror/PDFs/WhitePapers/Compression%20101.pdf and "Detection and the Dynamics Duo (Or Why Do Some Compressors Sound Great While Others Just Plain Don’t?)" at http://www.dbxpro.com/ftp_mirror/PDFs/WhitePapers/DetectionandDynamicsDuo.pdf

I use C1 comp-sc.

ThanksFor your Guidance!!