There are two distinct ways in which an artist creates his works. He proceeds from universal to the particular or from the particular to the universal. In the case of the imagery of the deity it is the first case. It is called Dhyatva Kuryat, the intellectual conception precedes the actual creation of work.
For example, in the imagery of Brahma, apart from representing all the lakshanas(symbols) like the four heads, four hands, lotus etc, one must make sure that the real essence of the deity is represented. Brahma is basically a Rajasik(active) deity always involved in the action of creation of universe. Hence any depiction of him as being extremely violent bordering on Tamas(inertia) or extreme sweetness and serene bordering on Sattva(equipoise) should be avoided.
Another example is that of Hanuman, the essence of Hanuman exemplifies Veera Bhava(heroic nature) and Dasya Bhava(attitude of a servant) that is one of extreme courage, strength and at the same time humility and simplicity. It is important to keep in mind that a depiction of courage should not turn into a depiction of extreme violence or animalistic behavior.
The goal of any image of a deity is to be a medium on which the spectator can meditate on the essence of the deity. It is important for an artist to depict the essence properly in his works. A wrong portrayal of essence by an artist leads to a wrong conception of the deity in the heart of the spectator. Hence the portrayal of excesive mucsles to depict strength, excessive violence to depict virility and excessive sweetness to depict equipoise should be avoided.