Prior to Mass, ask the priest if he needs help. The pall should be taken to the back of the church so that someone (typically the family of the deceased) will drape it over the casket. The Paschal Candle should be lit. Some parishes place this close to where the casket will be.
What you will probably be doing is asssting the celebrant when the body arrives at the church by holding the book and, I believe, the holy water in order for him to bless the casket (read: deceased).
Once the body has been received and draped with the pall, the procession begins (hopefully, there will be music; if there is none, the celebrant can chant something). You will be walking with the priest. If there are more servers, someone should carry the processional cross. The Mass proceeds in the usual manner after the opening prayer. If the celebrant is going to use incense, have it ready for the offertory and then towards the end.
I believe that a funeral Mass is the only time that incense is used at the end of the Mass as the casket is incensed. At this point, the In Paradisium is sung/chanted (at least that is what my parochial vicar does).
