How to set up an altar?

Worship of Radha and Krishna is no cheap thing. It cannot be done whimsically, but it must be very carefully executed under strict regulation. Not that there can be LSD taking and all sinful activities, and then Deity worship. I have made it a point that unless one is able to keep to the same standard that is kept here at the temple, he should not worship the Deity separately. Best thing is to keep a Guru-Gauranga altar at home and take part in the Deity worship program at the temple.

Letter to: Caitanya, Los Angeles, 25 April, 1973

In this quote Srila Prabhupada warns us not to take to the Deity worship whimsically. It is a serious matter and it needs to be executed according to strict rules and regulations. One of the conditions for worshipping a Deity (whether Radha Krsna Deity or Nitai Gauranga Deity) at the present moment is that a person must be second- initiated(must undergo a Gayatri initiation) under the rtvik system set up by Srila Prabhupada. This is evident from Srila Prabhupada's letter to Yamuna Devi Dasi from 1970:

Regarding an assistant Pujari, Ilavati may be trained to assist you, but she may not conduct Arcana without being dvija. The system is that only one who is qualified with Gayatri initiation may directly worship the Deities (i.e. bathing, offering bhoga and aratrik, cooking for the Deities, etc.). But she may assist you by helping in all other respects. If for some reason you are unable to perform aratrik, there are other devotees, initiated brahmanas, who can make the offerings there.

Letter to: Yamuna, Los Angeles, 2 March, 1970

Does that mean that people who are not yet up to this standard are barred from worshipping Krsna and making offering for Him? No. And that is why everyone and anyone can worship Him on his home altar in a picture form.

The basic altar consists of picture of 1.Panca Tattva, 2.Srila Prabhupada, 3.the previous acaryas-members of the disciplic succesion (positioned from left to right starting with the most recent ones such as Srila Prabhupada)and a picture of Lord Nrshimhadeva. The pictures of these personalities can be placed on a cupboard, table, shelf, or practically anything which you will be able to put your offerings on. The altar should be very clean and you should be able to clean it with a wet cloth. The altar cannot be used for anything else, but for the offerings, so make sure you can sacrifice it for Krsna for good. Not only should the altar be clean, but also the place where the altar is.  In the material(relative) world, the picture of a person and a person himself are two different things, however that is not the case with the Lord who is of an absolute nature. As such Krsna, as well as spiritual master Srila Prabhupada, is non-different from His picture. We should keep this in mind when we worship Them on the altar. The altar is an essential inspiration in Hare Krsna mahamantra mediation. One can offer an incense, a candle, on the altar or decorate with flower and in this way a transcendental atmoshpere is evoked.

A little bit about the personalities on the pictures:

More quotes of Srila Prabhupada on the matter

As far as staying in some boys apartment, this is permissable if everyone in the house agrees to follow the principles while you are there. That is no smoking, no drinking, etc. You may also install a small altar there with a picture of Guru and Gauranga and the Spiritual Masters there and perform mangala arati every morning and hold classes etc. Under these circumstances you can live in others apartments.

Melbourne, 10 February, 1973

The conch shells as you have described may be kept on the altar as decoration, but they must be kept clean.  Everything on the altar must always be clean.

Letter to: Govardhan 4,Juhu, Bombay-54, 18 November, 1973

Your desire to keep a personal temple room in your home is commendable, and you can do that in any case, wherever you are, by keeping an altar and offering your food to the Lord as prasadam.

Letter to: Kanu Gandhi, Bombay, 26 March, 1974