Covering ALL Of The Body
It is an agreed position by many respected scholars that the face and hands of the woman must be covered. Some scholars say it is permissible to uncover the face and the hands of the woman as long as there is no fitna (infatuation) caused by this action. Two things must be taken into consideration.
a) if she is beautiful and beautifies her face and hands with external substances, or
b) the society around her is corrupt where men do not lower their gaze, then it is prohibited for her to uncover her face and hands.
On the authority of the wife of the prophet (pbuh), Umm Salama (RA) said:
"When the verse was revealed that they should cast their outer garments over their bodies' was revealed, the women of Ansar came out as if they had crows over their heads by wearing outer garments.

The hijab must not be a display
The hijab itself must not be a display. Allah ordained it so as to cover the beauty of women and not for showing off. Allah (swt) says `And not show of their adornment except only that which is apparent.' (S24:31).
AND
`And stay in your houses and do not display yourselves like that of the times of ignorance.' (S33:33).
It is in no way logical that the hijab itself be a source of display.

The hijab must not be transparent The purpose of wearing hijab must be achieved. In order for the hijab to be a cover, it must not be made of transparent material making the woman covered only by name, while in reality she is naked. The prophet (pbuh) is quoted as saying: "In the latest part of my Ummah (nation of Muslims) there shall be women who would be naked in spite of being dressed, they have their hair high like the humps of the Bukht camel, curse them, for they are cursed. They will not enter Al-Jannah and would not even perceive its odour, although it's fragrance can be perceived from a distance of 500 years travelling by camel" This indicates that a woman could cause herself a grave and destructive sin if she puts on a garment that is thin and transparent and which clearly shapes her body's features.

Hijab must be roomy, and not tight.
The hijab is a safeguard against fitna. If it is tight, it will be descriptive of the woman's body and this violates and defeats the whole purpose of hijab.

The hijab must not be perfumed
On the authority of Ad'Diya Al-Maqdisi, the prophet (pbuh) said:
"Any woman who perfumes herself and passes by some people that they smell her scent, then she is a Zaniyah (adulteress)."

The hijab shouldn't resemble the dress of a man
Imam Ahmed, an-Nissa'ee reported the prophet (pbuh) to have said: "Women who assume the manners of men are not from us and also those of men who assume the manners of women." Abu Huraira narrated that: "The Prophet (pbuh) CURSED the man who wears the dress of a woman and the woman who wears the dress of a man."

The hijab must not resemble the garments of the kuffar
Abu Dawoud and Ahmed have related the prophet (pbuh) said: "The one who take the similitude (manner) of a certain people, then he/she becomes one of them."
Abdullah bin Ummar (RA) said: "The Prophet (pbuh) saw me wearing two garments dyed in saffron (orange), whereupon he said: these are the clothes (usually worn) by the kuffar, so do not wear them."

The hijab should not be for fame
Abu Dawoud and Ibn Majah have related the prophet to saying: "The one who wears a garment designed for a worldly fame, Allah will make them wear a garment of humility on the Day Of Resurrection then he will be set ablaze." The garment of fame is any garment a person wears to make themselves look famous. This applies whether the garment is highly precious and shows admiration to the life of this world or if it is chosen of a low quality to show lack of interest to this worldly life. The person may put on clothes with distinct colours so as to draw attention, act proudly and/or arrogantly.

Concealed ways of display
Examining the various conditions about the hijab one can clearly recognise that many of the young Muslim women are not fulfilling these conditions. Many just take "half-way" measures, which not only mocks the community in which she lives, but also mocks the commands of Allah (swt). They consider what they put on now wrongly as "hijab" So, O muslimoon, be mindful to Allah (swt) and His Messenger (pbuh), and do not deceived by those who "bless" this action of yours and conceal their true intentions. Do not be deceived, and there is no excuse to follow the evil.
If you are sincere in achieving Al-Jannah, then be mindful of these things, insha'allah .