Picatrix, while being a compilation of a wide variety of magical, religious and astrological practice, is heavily reliant on the celestial religion and magic of the Harranian Sabians.
The Harranians, whose antecedents and actual practice are mysterious, appear to be pagans, who survived into the Middle Ages under the Christians and then Muslims. While preserving indigenous beliefs and practices, they also venerated the stars and planets.
While Agrippa included summaries of many astrological talisman recipes from Picatrix, what he generally left out were the celestial rituals necessary to invoke the spirits of the stars and planets and to consecrate talismans. The most prominent example of the rituals and ritual practice of the Harranian Sabians is found in Book III, chapter 7 of Picatrix.
When we return to these recitations of the rituals and invocations of the Harranians, we see that while they can be used as petition for things or events desired, that they are at their root, religious and an expression of devotion to the celestial spirits.
Here are the introductory instructions,
"When you desire to speak with any planet or ask it for anything that you need, first and above all else, purify your will and your faith in God, and beware especially that you believe in no other; then cleanse your body and your garments of all dirt. Then determine the nature of the planet to which your petition corresponds. When you wish to address the planet to which your petition properly belongs, dress in clothing dyed the color of that planet, and suffumigate yourself with its suffumigation, and pray its prayer. Do all this when the planet is established in its dignities and called superior in its dispositions, for by observing these things, what you desire will come to pass."
Picatrix Bk III, ch. 7
Note that these instructions are for when you wish to speak with the planets OR ask them for something. It's a good idea to build up a positive relationship as opposed to just invoking them when you want something. The religious aspects are indicated by the need for both physical and spirituality purity. This is very common, in Shinto practice, there is always a chizuya, or water purification font, at the entrance to a shrine so you can wash your hands. See Chizuya.
Next, if you are asking for something you need to figure out what planet rules that thing. No use in asking Saturn for love!
Then the basic ceremonial preparation. One classic Harranian method is to wear appropriate clothing, in particular to wear the color associated with the planet. These can be widely variant, but often Saturn is black;Jupiter blue, green or purple, Mars, red; Sun yellow, orange or saffron, Venus, white, green, pink; Mercury, mixed colors; Moon, white or silver.
Then the suffumigation, this is appropriate incense. Again there are many different planetary incenses. If possible, however, it is important to use some kind of incense. If you have respiratory problems, you can pass on it, but even though I am sensitive I still use a very small amount.
Finally, and this is key for astral religion and astrological magic, we invoke the planets at an appropriate time. Planetary days and hours appear in the Greek Magical Papyri, but the Harranians appear to have been the most sophisticated users of electional astrology for magic and religion, timing their rituals and talisman making with full chart elections.