Your altar has to have a picture of the person you are honoring. The altar should have three tiers and be covered with brightly colored paper with cutout designs. Some suggestions are purple to represent pain, white to represent hope, and pink to represent celebration. Your altar can have candles all over it, but it's especially important to have four candles on the top tier to represent the four cardinal points. The before mentioned colors can be kept in mind for the candles, as well. The candles will light the way for the dead. The second level should have three skulls representing the holy trinity. A large skull should be placed in the center of the third level that represents the giver of life. You should burn incense in a "sahumerio" to get rid of bad spirits and clear the path for the dead. A cross of ash will expel the guilt of the ghost when stepped on. You should place food on your altar, pan de muerto, fruit and candy. You should leave a pitcher of water for quenching thirst, and a bottle of liquor for remembering good times. The ghost may want to wash up after their long trip, so a towel, a bowl and some soap should be left on the altar. Flowers can be used to decorate the altar, and give a pleasant scent.
The pictures I found of altars didn't follow this format exactly, but they were very bright and pretty. I noticed that the color orange was used a lot, and I also noticed that when skeletons were included on the altar, they were far from morbid. They wore headpieces or held musical instruments, and were really light-hearted. I also noticed pictures were used of Our Lady of Guadalupe, and other significant religious figures. I saw that some altars had lots and lots of food, and some very little.
I would like to see pictures of more altars, and especially altars from different regions of Mexico, as I'm interested in how they might differ. I'd also be interested in seeing how the Day of the Dead celebrations themselves differ from region to region. It sounds like a fun celebration and so different than anything we do here in the United States. Halloween is more of a "dress-up and get candy thing", and I think that Mexico's holiday sounds so much more interesting and meaningful.