A wee bit of knowledge in this area...
1) Start with some reworking of the OT, remembering that Judaism was, at one point, a polytheistic religion. Work that back in.
2) Jesus...eh. Gets complicated, depending on who you ask, so I'll subsection this.
a) If you're dealing with a Christian who does witchcraft, you can have a completely orthodox view of Jesus, the Trinity, etc., with some candle magic, tarot, and such thrown in.
b) If you're talking about an authentic, mid-eastern pagan who has included Jesus in their theology, things go on from here, depending...more subsections...
i) Jesus is a spiritual ideal and metaphor, not a real person.
ii) Jesus is an ascended teacher, master, etc.
iii) My favorite I've heard...Jesus was a Thelemic prophet whose message was horribly distorted over the years.
iv) Jesus is the son of the goddess.
v) Jesus is deity, inasmuch as we are ALL deity. He just realized this and was able to act like a deity on earth.
3) Throw out eternal punishment, original sin (unless you redefine sin...usually to ignorance rather than incorrect behavior...then go NaChSh = MaShYCh and have your head explode with TEH CABALAZ!), and have some fun with the first commandment (No other Gods before you? Can I have other Gods, if they come after you? Doesn't say I can't! WIN!), and, y'know, reinterpret the Bible as much as any other Christian does, but to a different end.
4) Generally, but not always, get a big devotion to the Virgin Mary, Mary Magdalene, and St. Sophia.
Now, that's more an overview of ChristoPaganism, but the same general techniques can be applied to merging Christianity with any specific pagan path.
The christopagans. I have married them.