Every spirit should be rewarded some form of offering for the services rendered unto the magician/sorcerer. But offerings should differ accordingly, as each spirit has a class each offering needs to be particular to the spirit's nature and be presented in an intelligent and formal fashion.
So here is my personal formula:
Super-celestial and Celestial Spirits:
+Angels receive a set period(days, weeks, months) of prayerful praise at one's oratory altar. The words themselves are the offerings, but candles and religious/biblical incense which has been consecrated according to the arts of Solomon or the Church may also be used in conjunction to the prayers.
Sub-celestial, Aerial, Terrestrial, and Infernal Spirits:
+Aerial Spirits are of mixed natures and thus the way one places offerings unto these spirits differ for the individual spirit that was used. The more gracious of the aerial spirits may have their seal placed near the oratory altar in which the spirit receives praise and thanks for a period of time. If the aerial is more of the unruly kind, it is better for the magician/sorcerer to draw their seal at a crossroads and offer praise and thanks there..