So first I walked through the house, room by room, burning herbs associated with cleansing. In general I recommend using a combination of vervain, rosemary, and juniper when possible, but any one of those alone is also good. Using smoke to purify and bless spaces and the home is an old Celtic practice, particularly using juniper. F. Marian McNeill in the Silver Bough says "Juniper, or the mountain yew, was burned by the Highlanders both in the house and in the byre as a purification rite on New Year's morning" and the Gadelica itself says "Iubhar beinne [juniper] and caorran, mountain ash or rowan, were burnt on the doorstep of the byre on the first day of the quarter, on Beltaine Day and Hallowmas." Likewise rosemary also has a strong historical association with cleansing, as according to Grieve's Modern Herbal it was burned to cleanse a sick room and was also believed to remove any evil influences in general (http://botanical.com/botanical/mgmh/r/rosema17.html). Vervain in both the Celtic and Roman world was considered a sacred herb and used as an offering to the Gods (http://botanical.com/botanical/mgmh/v/vervai08.html)
Next I lit a white candle and walked through each room again praying for blessing on the home. This is based on traditions associated with certain holidays, like Samhain, where fire - usually in the form of a burning torch - would be taken around the boundary of a property to bless it and protect it.
In the end I stood in the middle of what would be the living room, holding the candle, and recited a prayer modified from the Carmina Gadelica:
"Gods bless this house,
From site to stay,
From beam to wall,
From end to end,
From ridge to basement,
From balk to roof,
From foundation to summit,
Foundation and summit."
House Blessing 45
God bless the house,
From site to stay,
From beam to wall,
From end to end,
From ridge to basement,
From balk to roof-tree,
From found to summit,
Found and summit.
References:
The Silver Bough by F. Marian McNeill
Carmina Gadelica by A. Carmichael
a Modern Herbal by M. Grieve
By Land, Sea, and Sky by M. Daimler