Ifa teaches that the power to effectively invoke Spirits comes as a result of initiation and the training that is sanctioned by initiation. The exception to this rule is egun (ancestor spirits).
In Ifa, there are ancestor initiations (egungun, isegun, ato), but everyone is believed to have the power and the ability to communicate with the spirit of those blood relatives who have passed beyond this life. Communication with your own ancestors is a birthright. At times this communication can simply involve remembering a revered ancestor and making use of the memory as a basis for making life decisions. In many ways ancestor communication is an extension of the training and wisdom we receive from our parents.
Ifa says you cannot know who you are if you cannot call the names of your ancestors going back seven generations. Remembering names is more than reciting a genealogy, it is preserving the history of a family lineage and the memory of those good deeds that allowed to the family to survive and create a home for the continued cycle of reincarnation (atunwa).
In Yoruba culture it is common for the uninitiated to make direct contract with ancestor spirits. The most prevalent process of communication is through dreams. Communication also occurs during participation in annual ancestor festivals. Because such festivals are not common in this country, Ifa worshipers in the West have created several viable alternatives. Using these alternative methods, the first step in the process of honoring the ancestors is the construction of an ancestor shrine used as a focal point for prayer and meditation.
There are a number of traditional African methods for building an ancestor shrine, some of which are very complex and require personal training. For example it is common in traditional Yoruba culture to bury revered ancestors under the floors of the family home. The tomb of the ancestor is the foundation of the ancestral shrine.
For those who do not have access to lineage elders, I recommend the ancestor alter be constructed with minimal elements (in some lineages in the Diaspora there is a standardized method for building a shrine, these methods vary from family to family and should be followed according to lineage tradition). Once the basic elements are in place, the ancestors can be contracted directly for guidance on further additions to the shrine. In other words once you are in communication with the ancestors they will tell you if they want specific items brought to the shrine.
Source : Ancestor Reverence by Awo Ifayemi