to contact a loa
While I admit, not being one for voodoo, I have not tried this, though it seems legit from what I've seen.
(I don't own this info, as it is basic voodoo with a few addition)
A shrine set up in honour of one (or more) loa(s) with images, items, incense, etc appropriate for them
This is not something for begginners, and I suggest basic techniques practiced before attempting this, although it does make a good first voodoo spell.
First decide which Loa you wish to work with. Perhaps the best one to work with first is Pappa Legba, as he is the gate keeper and through him you can commune with all loas and spirits. Research your chosen loa, and find out what their tastes are. Select with this info an appropriate offering. Now, at a time which is appropriate for the loa your working with, place the offering on the shrine, light any candles and burn any incense you have, then meditate on the loa you wish to reach. Vibrate their name. When you feel their presence, first welcome them to your home. Remember, you are playing host to important guests. Present them with your offering, and say you hope they find it appropriate. Then ask them of any favour you have which yo feel is respectful. Remember to ask, and for fucks sake, be polite! (You could just perform this ritual to present them an offering without asking a request, and that's fine) When you are done, thank them for their time, and say they may return to their home if they wish. Sometimes, they may choose to hang around. Perform a grounding, and if you are uncomfortable with the energies still around, perform a banishing or cleansing ritual.
If you wish to do this with a loa other than Pappa Legba, you must first invoke him, ask him to help you communicate with the loa you wish to speak with, than through him invoke the loa. Both will need an offering and a thanking.