བསུར། sur 

The Tibetan word “sur” refers to the smell of roasted flour that is offered to spirits. The best times for practicing sur are in the evening or at night. You do this practice during a break from sitting meditation-not a break time from Dharma practice but a break time from sitting meditation. The text says “night time”; I think that evening or night time are best because these are the times when spirits wander. This is also the time when dakinis gather. It’s easier for the intermediate state beings to get what you offer at those times. If you cannot do it at those times, then other times are acceptable, but those are best.
The container used for sur practice should be clean and unbroken. The fire shouldn’t have much smoke. If you make fire with firewood, then usually there’s smoke. If there’s a lot of smoke, then you don’t smell the food because the smoke overwhelms the scent of the food. The food scent gets mixed in the smoke, the smoke’s stronger, and so they might not receive the food.
So, reduce the smoke as much as possible. Let it burn as much as possible until there’s either no smoke at all or very little smoke. The less smoke the better so that the spirits can smell the food. When they smell the food and when you chant the mantra they get something. When the coals are red inside with some white flecks outside, that’s good. So then put food on top of the burning coals.
It’s excellent if you can do this practice every day. If you do it occasionally, then that is OK also. However, if you do it consistently and then stop it’s not so good because the hungry ghosts get into the habit of being fed every day and then they come and there’s no food.
Also, when making offerings to hungry ghosts, it’s good to cover your eyes. We traditionally wear a hat with black threads or strands hanging down to cover our eyes when offering to hungry ghosts. When hungry ghosts see a human body and human face, it appears so powerful and magnificent that they get scared, just as we would get scared if we saw a lion in the jungle. So, we wear these things when making charity to them so that they won’t get scared away.