Hekate's Deipna are meal offerings made to Hekate at the triple crossroads on the last night of each lunar month. In its most basic form today one can simply make offerings to her on this night, if that's all your circumstances will allow. However the event itself is much more elaborate and I encourage you to do as much as you can.
First, you should clean Hekate's altar or the area where you will honor her (this would be your main altar if you use one for all the Gods). This can be done earlier in the day or right before the ritual. I find doing it earlier adds to the anticipation of the coming rite and lends an air of festivity. Save what you clear away because it will be part of her offering. Depending on the substance it can be burnt in a charcoal burner or added to the plate of food. Some examples of things you may gathering in your cleaning are dirt, dust, candle drippings, bits of cloth or string, etc. Another part of the pre-ritual clear out is pulling together anything left over from the previous month's offerings. For example if you made libations of wine but still have some left over in the bottle you should offer this to Hekate. Likewise if you had a bowl of barley and used only a portion the rest should be offered to Hekate. This process clears out the old month entirely. Everything will be burnt or go into the dinner.
For the ritual itself you will need an offering plate and incense burner, charcoal briquette, and incense at the very least. I also like to have a candle, wine, libation cup, and an image of Hekate - a statue or framed picture (even one printed from the internet will suffice). And of course Hekate's supper. Traditionally the supper contains a sweet bread or cake, fish (sprat and mullet), garlic, eggs, and cheese. You can offer any or all of these as well as anything else you feel appropriate - for example, this is UPG but Hekate let me know she likes black olives so I usually include them. You should have everything ready beforehand to use during the ritual. Most charcoal briquettes will need several minutes to light and then a few more minutes before they are ready to use.
You may start with a self-purification, such as dipping your hands in khernips. Approach the altar, light her candle if you're offering one, and spend a few moments in contemplation. When you are ready, speak some words of praise or a hymn such as the Orphic Hymn to Hekate or passage 409ff. from Hesiod's Theogony. I've adapted her hymn from PGM IV 2520-2569 for use in this ritual.
If you have anything from your cleaning to burn you should place it on the charcoal first. Then add some incense. Pour a libation if you're offering one. And finally present her supper. You may say something like, "Hekate, I offer to you this incense, this wine, this (name each item)… Look kindly upon these offerings and accept them with joyous heart."
You can end the rite here or continue with the theme of cleansing and purification at the end of the month.
Prayer for purification: "Hekate, look kindly upon your supplicant who brings you offerings on this day as on many days in the past. Mighty Hekate, please take the foul and filth from this place. Clear it of all negativity and harm." This can be followed by fumigating your home. Place incense or herbs on the charcoal and carry the burner around the home - be careful, it will be hot and you may need protection for your hands! Make a circuit that brings you back to the altar. There you may make a prayer for Hekate's protection during the new month, like: "Hekate Propylaia, please grant me (us/my family/etc. as appropriate) your protection and keep all harm from entering my (our) home. For this I am (we are) eternally grateful."
When you have completed the ritual, gather the supper up and dispose of it. This should be at a triple crossroad but do the best you can. In some circumstances people are only able to place it outside in their yard or even just indoors in its own trash bag that is taken out immediately.
Finally, this is a good time to perform divination, especially if you specifically desire to ask Hekate about something.
The Orphic Hymns. Athanassakis, A.
The Greek Magical Papyri in Translation. Betz, Hans Deiter (ed.)