Factors required for validity of salaat

There are 29 factors necessary for Salaat to be valid:
1.Purity from major and minor impurity (also from menstruation and childbirth bleeding).
2. Purity of the body, clothing and place of Salaat from such a measure of filth that is not forgiven.
3. The places where the feet, hands, knees and forehead are to be placed have to be pure.
4.Satre Aurat covering of those parts that are prescribed by Shariat (navel to knee for men and complete body for women).
5.Facing the Qibla: a person who sees the Kaabah must face it and for those who do not see it, even if they are in Makkah, it is ‘obligatory’ only to face in the direction of the Kaabah.
6.Presence of the time of Salaat (obligatory).
7.To be firmly convinced that the time of Salaat has already started.
8.Niyyat (intention) of Salaat.
9.Saying “Allaahu Akbar” (Allaah is the greatest) – Tahrima at the start of Salaat without separating it from the intention (by speaking).
10. Saying Tahrima while standing, before going for Ruku (before bowing).
11. The Tahrima should be made before not the intention.
12. To recite the Tahrima so audibly that one cannot hear himself.
13. For the Muqtadi (one following the Imaam) to make intention of following the Imaam.
14. To specify which “obligatory” Salaat is being performed.
15. The intention for Wajib Salaat has to be specifying of Nafl Salaat is not compulsory.
16. To stand for the Fardh and Waajib Salaat. One is allowed to sit for Nafl Salaat even without an excuse.
17. Qiraat (recitation of Quraan) even though it be one Ayat in the first 2 Rakaats of the Fardh Salaats and in every Rakaat of the Nafl Sunnat and Witr Salaats.

There are no specified portions of the Quraan to be read for the Salaat to be valid. The
Muqtadi should not recite anything but should listen attentively to the Imaam and remain silent.

 If he reads any Qiraat it will be Makrooh Tahrimi.

18. Ruku (Head and hips to be on equal level for males).
19. Sajdah should be made on a hard surface that can be felt and upon which the forehead remains stable and firm even though it be upon one’s palm or the edge of a cloth. The place of Sajdah must be Paak (clean). It is necessary to prostrate with the hard part of the nose and the forehead. 

Prostration by the nose only is not correct except if the forehead is injured, etc.

20. The place of prostration must not be more elevated by more than half a cubit from the place of the feet.

 If so then prostration is not valid, except in huge crowds where one is forced to prostrate on the back of another who is performing the same Salaat.
21. To place the hands and knees on the same surface whilst in Sajdah.
22. To place at least some part of the toes on the surface. To place only the outer position of the feet on the surface will not suffice.
23. Bowing (Ruku) must precede Sajdah (prostration).
24.To rise from Sajdah to a position close to sitting.
25. To return from sitting posture the second Sajdah.
26. To sit for the Qaidah Aakhirah (last sitting) to the extent of time in which at least the Tashahhud can be read.
27. Performing the Qaidah Aakhirah (last sitting) after all acts of Salaat.
28. Performing all acts of Salaat whilst awake.
29. To have full knowledge of the procedure of Salaat and all its Fardh aspects so that one knows the Sunnat aspects, and one doe not perform a Fardh with the intention of Nafl, etc.

The Fardh acts during Salaat are:

a. Qiyam (standing)
b. Qirat (reciting of a Quranic verse)
c. Sajdah
Some mention that Qaaidah Aakhirah (as explained in (24) is also Fardh.

Wajib acts of Salaat:

There are 18 Wajib acts of Salaat:

1. Recitation of Surah Fatiha.
2. Reciting any other long Ayat or 3 short Ayats to Surah Fathiha in the first 2 Rakaats of the Fardh Salaat and in all Rakaats of the Witr, Sunnat and Nafl Salaats.
3. Specifying the reading of the Sura Fatiha for the first 2 Rakaats of the Fardh Salaat.
4. To recite Surah Fatiha before the Surah (Ayat).
5. To make Sajdah with the nose and forehead.
6. To make the second Sajdah of the first Rakaat before proceeding to any other action.
7. To perform every posture with ease and calm.
8. To perform the first sitting (Qaidah Aula).
9. To recite the Tashahhud in the first sitting (Qaidah Aula first sitting after 2 Rakaats).
10. To recite the Tashahhud in the last sitting.
11. To stand immediately for the 3rd Rakaat after the Tashahhud (with out delay).
12. Making Salaam 2 times (once to the right and one to the left), to say the words “As Salaam” is Waajib, to say “Alaykum” is Sunnat e Muakkidah.
13. To read Dua e Qunoot in the Witr Salaat.
14. To recite Takbeer of the Eid Salaat.
15. Specification of the words Allaahu Akbar for the start of every Salaat except the two Eids.
16. To say the Takbeers of Ruku before going in Ruku in the second Rakaat of the 2 Eids.
17. For the Imaam to recite the Qiraat aloud in the following Salaats:
 Fajr, first two Rakaats of Magrib and Esha (even though Qaza), Jumuah, 2 Eids, Taraweeh and Witr of Ramadhaan.

18. To recite the Qirat silently in Zuhr, Asr, 3rd Rakaat of Magrib, 3rd and 4th Rakaat of Esha and all Nafl Salaats during the day.

The Munfarid (one performing Salaat alone and not in Jamaat) has the choice of reading audibly or not in those Salaats wherein Qiraat is audible.

 A person performing Nafl Salaat during the night also has this choice.

If a person omitted the recitation of a Surah in the first 2 Rakaats of Esha, he should read it audibly in the second two Rakaats with Surah Fatiha.

 However if Surah Fatiha was omitted it will not be repeated in the last two Rakaats, but
make Sajdah Sahw (prostration of forgetfulness).

source: Taleem ud Deen (Hanafi), Mufti Afzal Hoosen Elias.