These etiquettes are narrated in the Hadith. For reasons of brevity, only the following summary and reference of each Hadith is mentioned instead of the entire Hadith.
 

• To abstain from haraam food, clothing and earnings. (Muslim : Tirmidhi)

• To make Duaa with sincerity. In other words, one should firmly believe that nobody but Allah Ta'aala will fulfill his objectives. (Haakim)

• One should perform a good deed prior to making the Duaa & he should mention this during the course of the Duaa. For eg. He should say, O Allah! I had performed so & so deed solely for Your pleasure. O Allah! accept my Duaa due to the barkat of that deed. (Muslim, Tirmidhi, Abu Dawud).

• To make Duaa whilst one is paak & clean. (Tirmidhi, Abu Dawud, Ibn Majah, Nasai, Ibn Hibbaan, Mustadrak).

• To make wudhu before the Duaa (All six major hadith collections)

• To face the Qiblah (All six major hadith collections)

• To sit as in the Tashahhud position (Abu Awanah)

• To praise Allah Ta'aala at the beginning as well as at the end of Duaa (All six major hadith collections)

• To convey Durood upon Rasulullah (saw) at the beginning as well as the end. (Abu Dawud, Musnade-Ahmad)

• To spread out both the hands. (Tirmidhi, Mustadrak)

• To raise both the hands up to the shoulders (Abu Dawud, Musnade-Ahmad)

• To sit with humility and respect. (Muslim, Abu Dawud, Tirmidhi, Abu Dawud)

• To mention ones helplessness and dependence. (Tirmidhi)

• To abstain from raising the eyes towards the sky whilst making Duaa (Muslim)

• To mention the Asmaal-Husnaa (the names of Allah Ta'aala) and the sublime qualities Of Allah Ta'aala. (Ibn Hibbaan and Mustadrak)

• To abstain from ceremonies rhyming of the Duaa phrases (Bukhari)

• To abstain from saying the Duaa in a "sing-song" tone if the Duaa is in a poetic form (Hisn)

• One should make Duaa through the medium of the Ambiyaa (alayhimus-salaam) and other Pious servants. (For eg. He should say. O Allah! Accepts my Duaa through The good offices of these saintly people). (Bukhari, Bazzaar, Haakim)

• To make the Duaa in a soft voice (All six major hadith collections on the authority if Abu Musa)

• To utter the Duaa phrases transcrIbnd from Rasulullah Sallalahu Alayhi Wasallam because Rasulullah Didn't leave out a single need of the Deen nor of the dunya whilst teaching us how to make Duaa (Abu Dawud/Nasai)

• To make a Duaa that encompasses most of the needs of Deen and the dunya. (Abu Dawud)

• To make Duaa in favour of oneself first, thereafter ones parents and to include the other Muslims in the Duaa as well (Muslims)

• If the Imam is making Duaa, he should not make Duaa for himself only but he should Include all the congregants in the Duaa (Abu Dawud, Tirmidhi, Ibn Majah)

• Abu Dawud (R.A.) Narrates that Rasulullah Said that the Imam who makes Duaa for himself only, has betrayed the people." In other words, the Imam should not Make a Duaa that is restricted to him alone. For eg. He should not say, "O Allah! cure my son." or "O Allah! Return my lost item." etc. but he should make a Duaa that includes all the congregation for eg. He may say "O Allah! Forgive us and have mercy upon us."

• To make Duaa with firm conviction (for eg. he should not say: "O Allah! If you wish fulfil so and so task of mine." (All six major hadith collections)

• To make Duaa with enthusiasm & yearning. (Ibn Hibbn & Abu Awana).

• As far as possible endeavour to bring about a "presence of heart and mind" and cherish a high hope of the Duaa being accepted.(Haakim)

• To make Duaa repeatedly. (Bukhari, Muslim)

• This repetition should be at least thrice (Abu Dawud)

• Note One may repeat the Duaa thrice in none sitting or he may repeat it on three different occasions. The "repetition of the Duaa" can be interpreted in both ways."

• To make Duaa earnestly and insistently. (Nasai, Hakim, Abu awanah)

• To abstain from making Duaa of severing family ties or other sins. (Muslim, Tirmidhi)

• Avoid making Duaas of pre-determined and fixed things (for eg woman should not make a duaa of being transformed into a man or a tall person shouldn't make Duaa thus:"O Allah! Make me short ." etc) (Nasai).

• Don't Make Duaa for impossible things. (Bukhari)

• Don't make a Duaa in which you ask Allah Ta'aala to confine His mercy to yourself Only (Bukhari, Abu Dawud, Nasai, Ibn Majah)

• Ask only Allah Ta'aala alone for all your needs. Do not depend upon His creation. (Tirmidhi/Ibn Hibbaan)

• The one making the Duaa as well as the person listening to it, both should say Aameen at the end. (Bukhari, Muslim, Abu Dawud, Nasai)

• Rub both hands over the face at the termination of the Duaa (Abu Dawud, Tirmidhi,Ibn Hibbaan, Majah, Hakim)

• Don't be impatient over the acceptance of Duaas. In other words, don't say: "I've made Duaa repeatedly but to no avail." (Bukhari, Muslim, Abu Dawud, Nasai, Ibn Majah)

From Sidi Faraz Rabbani of the Hanafi fiqh list.