We should first address the question: why photograph nudes at all?  

(The corollary: “Why nude?” is answered in Appendix I.)  

While everyone has their own motives, mine are simple:
The artistic nude is the most challenging — and rewarding — of all photographic genres.
The goal of the artistic nude is to present the human form as the pinnacle of creation — with beauty, truth, and goodness.  It’s about celebrating the body with respect and wonder. Presenting the female form with its graceful lines,  sensual curves, gentle softness, a vulnerability, and a quiet dignity; the male form with a presence that conveys protection, resilience and confidence.  
What may look simple is actually one of the greatest challenges in photography. It asks the artist to go far beyond photographing a person and instead capture something deeper — the individual beauty and humanity of the body itself.
Before getting practical, we must address the three biggest lies regarding nudity that have infected our culture:
    1. Nudity is inherently sexual.
    2. Exposure to nudity will trigger sexual thoughts.
    3. The desire to view nudity reveals a moral weakness or a character deficiency.
These lies were spawned in the Victorian war on vice, having originated in the Gnostic heresies of the first century. Summary: human body is evil, thus any depiction of the bare human body will lead to sin. The result was a set of rules that not even the Victorians could follow.

Lie #1  Nudity is sexual.
This lie is was spawned in the Victorian Age based on a misunderstanding of the story of Adam and Eve in the garden.  Adam and Eve projected their shame onto their nakedness and tried to cover themselves.  Believe it or not, the Bible never makes a moral issue out of nudity! Indeed, God orders Isaiah to preach in the nude (for three years!) David and Saul both prophesied and danced before the Lord in the nude or near-nude.

Nor does history support this idea. Study art prior to about 1800. Start with the Sistine Chapel. Their culture appreciated the artistic nude when used to reveal truth and beauty. For them, nudity did not equate to sex, neither should it for us.

Some will argue that the sexual aspect of nudity is programmed into our DNA.  But all the evidence contradicts this claim. Many cultures, both past and present, treat nudity with little or no sexual implications.  Numerous societies practiced (and some still do) mixed nude bathing, sports and toilets. The women of the Minoan culture wore dresses that covered their backs but left their breasts exposed! Even today, Zulu girls will dance topless at school events.

Lie #2 Irresistible Lust
We’ve been trained, much like Pavlov’s dogs, to expect to lust!  For generations, we’ve been taught that men are visually stimulated and can’t help themselves. While men are generally more visually oriented than women — which explains why we’re better hunters (and drivers) — women are not exempt from these temptations. They just hide it better.

One simple example disproves this lie: medical professionals deal with naked people almost everyday without lusting. Indeed, I remember the night my son was born. I was making small talk with the doctor as he stitched up my wife. For him, it was just another night on the job.

Lie #3  Moral Weakness:
Appreciating nudity is not a character flaw, quite the opposite, it’s a design feature! Your brain responds within milliseconds of seeing an attractive person!  It floods itself with dopamine, oxytocin and other endorphins.  Your brain was designed to appreciate beauty. Don’t fight it, learn to master it.

The initial responses are basically neutral, just an intellectual recognition of beauty.  How we respond to this rush of “feel good” chemicals determines whether we celebrate God’s creation or fall into carnal perversion. In fact, this is the mechanism that leads to porn addiction and is very similar to a gambling addiction! It’s up to the viewer to decide how to respond.

Practical Application:
Here’s my definition of art vs porn:

       If the focus is on the body’s form, it’s art.

        If the focus is the body’s function, it’s porn.

Let me expand on this: if the artwork is showcasing the shapes, curves, and beauty of the human body, it’s art; if it’s primarily about sexual functions, it’s porn.

Here’s the practical application:
    1. Portray women with emphasis on beauty, innocence, and dignity.
    2. Portray men with strength, power, and purpose.
    3. Never show any sexual activity.
    4. Genitals have very little artistic value, keep them in the shadows.
       
 Additionally, one must stay professional at all times and follow standard industry practices:
    1. Never work with a model (clothed or not) alone.
    2. No physical contact.
    3. No innuendos or off color comments.
    4. Clearly communicate expectations.

The artistic nude is not automatically immoral. Like any form of art, its morality is dependent on the motives of both its creator and beholder. We must learn to see the human form not with shame or lust, but with the wonder it deserves as the pinnacle of God’s creation.

Here's a longer theological explanation: 
NSFW Christianity