Looking into the other person's eyes, clinking with contact (or without it, as the Americans do), avoiding crossing arms with the other guests, saying 'cheers', 'your very good health' or 'chin chin'... There are countless rules for toasting which depend on where you are and who you are with. 

In France, where champagne is made, it is highly recommended to look directly into the eyes of the person whose glass you are clinking.