It is always best to scry at night, because this method of divination is closely related to the Moon and all other Lunar correspondences. If you are indoors, you should extinguish all of the lights except for one candle. The candle should be out of your line of sight when you are looking at your scrying tool. Above and behind you is a good placement. Some people prefer that the candle flame flickers, others like the flame to remain still. Experiment and see what you like.
The room should be as quiet as you can make it. If you live in an apartment or with someone else, some quiet instrumental music can be used to drown out any unwanted sounds. Don’t use music with lyrics, because at the least, the lyrics might influence your visions. At the most, they might prevent you from concentrating enough to see anything.
Make sure that you will not be disturbed, and figure out a comfortable way to sit either holding your scrying tool or with it resting before you on the floor or a table.
If you are scrying on a particular subject, you might get better results if you schedule your scrying time for when the Moon is aspected favorably to the corresponding planet. Visions are always stronger around the time of the full Moon.