Below is the protocol I follow for chemical shift referencing (direct for 1H, and indirect for 13C and 15N). Actually I always have to look back and forth for referencing, so thought why not make a small script and put it on web so that the access becomes handy.

!!! The referencing should be done on the day of recording experiments !!!

!!! No rounding off of frequency numbers !!!

1. Record a one-D (1H) spectrum (s2pul on Varian and zg on Bruker) of the buffer (or sample) containing DSS.
2. Set the cursor on the right most line (DSS line) in the 1H spectrum of the sample. For Varian, type rl(0p) to set the DSS line to 0 ppm. In Bruker, use one of the buttons on the top panel to do the same.
3. Type movetof (Varian) to set the tof at DSS line. In Bruker, use one of the buttons on the top panel to set the O1 at DSS line.
4. Check the 1H frequency (spcfrq command in Varian will display four values, use the first one: RF Channel 1 (Obs) frequency). This frequency will be called as H⁰

Now,

1. For proton refrencing, check for frequency numbers against sfrq (Varian) or SFO1 (Bruker) values in the procpar file (Varian) or the acqu file (Bruker) of any experiment; call them as H^val.
2. For nitrogen refrencing, check for frequency numbers against dfrq2 (Varian) or SFO3 (Bruker) values in the procpar file (Varian) or the acqu file (Bruker) of any experiment; call them as N^val.
3. For carbon-aliphatic refrencing, check for frequency numbers against dfrq (Varian) or SFO2 (Bruker) values in the procpar file (Varian) or the acqu file (Bruker) of any of the HNCA, CBCANH type experiment; call them as CA^val.
4. For carbonyl refrencing, check for frequency numbers against dfrq (Varian) or SFO2 (Bruker) values in the procpar file (Varian) or the acqu file (Bruker) of HNCO and HN(CA)CO type experiment; call them as CO^val.

References:

1. Wishart et al, “1H, 13C and 15N chemical shift referencing in biomolecular NMR”, JBNMR (1995), 6, 135-140.
2. Wishart et al, “Protein chemical shift analysis: a practical guide”, Biochem. Cell Biol. (1998), 76, 153-163.