To sanctify is not a very big thing - the pectoral cross, ring, cake, or eggs for Easter - take them to Church. Do not have to coincide with it to any occasion. The temples are open to believers every day, and the ritual has nothing to do with dates.
If your cross standard, like the others, tie him to a bright ribbon or braid. At the same time will be sanctified few items, make sure not to confuse a thing with someone else. The cross purchased Church, is sanctified, to carry out the ritual again is not necessary.
Contact the priest before the Liturgy. If you failed to find it - ask for help from any employee of the Church. Typically, the staff responsible for the organization of rites, are behind the counter that sells icons and candles. Explain to him what is required. It will give things for the altar and the priest will announce it to him.
You may want to be present in the Church during singing. Try to renounce from worldly thoughts and think only about the spiritual. Read "In the name of the Father and of the Son and of the Holy spirit" and "the grace of the Holy spirit." Wait until the end of the service. Three times the priest will sprinkle the items with Holy water and read the corresponding case of the Psalms. After that, the thing is considered to be purified.
When the prayer ends, go to the priest for the consecrated crossOhm. Don't forget to thank him and to ask the blessing.