Just as a bus is the best place for abuse, you should ideally perform abasement in a basement. There is something about the subterranean nature of the location which lends itself to the embrace of personal wretchedness.
Obviously the basement must first be prepared with the installation of a shrine or altar to an enraged and merciless deity, for example the hideous bat-god Fatso, or Allah. Adherents of the latter usually claim he is all-merciful, but come on, we all know that is twaddle. Allah does as much smiting as Jehovah, and has an extremely lengthy list of harmless deeds he construes as wrongdoing. His sin-catalogue is almost as bulky as Fatso’s. Whether you choose Jehovah or Allah or Fatso is entirely up to you. The important thing is to have a focus for your grovelling in your basement.
Once you have installed your shrine or altar or whatsit, never again bother to sweep the floor of your basement with a broom. By allowing dust and debris to settle and moulder, you create an apt surface upon which to prostrate yourself, flat on your belly, while bewailing your utter worthlessness. If you have picked for your deity one of the ones that allows itself to be depicted by human hand, make sure the picture or icon is terrifying in its intensity and shows the god in a particularly bad temper. Actually, you can do this for one of the image-forbidding gods too, because by having wrought a picture of them you will just make them more enraged, and the angrier they are the better, as far as your abasement is concerned.
I hope it is clear why you should avoid a woolly liberal deity like gentle Jesus, in a chunky Church of England cardigan, whose reaction to your begrovelment would as likely as not be a compassionate smile and a helping hand to lift you from the grubby floor. If you are going to get the hang of this abasement business, you want to provoke wrath and scourges and plagues of locusts and thunderbolts.
There is no minimum time to spend face down in the muck in the dark of your basement. A properly vengeful and psychotic deity will not be assuaged with a mere ten or fifteen minutes here or there. Best to plan for the day, and night, and the following day, and the night again, at least. And no sneaking up to the kitchen for a snack. Unless, of course, it is a diet of worms.