Lancing Boils

Lancing boils is something your doctor will do, he will probably use a sterile syringe or needle and will make a small incision so that the pus will drain away.  He may well then pack the incision with guaze and antiseptic to keep away bacteria and this will also allow any excess pus to drain. 
 
If lancing boils is something you do yourself - then make sure everything is sterile.  I know that some people can't be bothered to go and see a medical practitioner so will lance the boil themselves.  Cleanliness is important if you lance the boil, make sure all equipment is sterile whether that is a needle or syringe and that all hands are clean.  Wash the area with antibacterial soap or apply an ointment to make sure that no further bacteria can enter the area.  Remember, it is of the utmost important to keep the area sterile or you could cause further complications.  If, in doubt, go and see your doctor.

Also if you have an underlying illness such as diabetes or other ailments - go let your doctor lance the boil to be on the safe side.