Praise be to Allaah.  

In a two-rak’ah prayer, the worshipper should say the Tashahhud, and this is one of the versions:

Al-Tahiyyaatu Lillaahi wa’l-salawaatu wa’l-tayyibaat. Al-salaamu ‘alayka ayyuha’l-Nabiyyu wa rahmat-Allaahi wa barakaatuhu. Al-salaamu ‘alaynaa wa ‘ala ‘ibaad-illaah il-saaliheen. Ash-hadu an laa ilaaha ill-Allaah wa ash-hadu anna Muhammadan ‘abduhu wa rasooluh (All compliments, prayers and pure words are due to Allaah. Peace be upon you, O Prophet, and the mercy of Allaah and His blessings. Peace be upon us and upon the righteous slaves of Allaah. I bear witness that there is no god except Allaah and I bear witness that Muhammad is His slave and Messenger).

(al-Bukhaari, 831; Muslim, 402).  

Then after that he should send blessings upon the Prophet (S) and say:  

“Allaahumma salli ‘ala Muhammad wa ‘ala aali Muhammad kama salayta ‘ala Ibraaheem wa ‘ala aali Ibraaheem, innaka hameedun majeed. Allaahumma baarika ‘ala Muhammad wa ‘ala aali Muhammad kama baarakta ‘ala Ibraaheem wa ‘ala aali Ibraaheem, innaka hameedun majeed (O Allaah, send prayers upon Muhammad and upon the family of Muhammad, as You sent prayers upon Ibraaheem and the family of Ibraaheem, You are indeed Worthy of Praise, Full of Glory. O Allaah, bless Muhammad and the family of Muhammad as You blessed Ibraaheem and the family of Ibraaheem, You are indeed Worthy of Praise, Full of Glory).

(al-Bukhaari, 3370; Muslim, 406).  

Then he should recite the following du’aa’:

Allaahumma inni a’oodhu bika min ‘adhaabi jahannam wa a’oodhu bika min ‘adhaab il-qabr, wa a’oodhu bika min fitnat il-maseeh il-dajjaal, wa a’oodhu bika min fitnat il-mahya wa’l-mamaat wa a’oodhu bika min al-ma’tham wa’l-maghram (O Allaah, I seek refuge in You from the torment of Hell, and I seek refuge in You from the torment of the grave, and I seek refuge in You from the tribulation of the Dajjal, and I seek refuge in You from the trials of life and death, and I seek refuge in You from falling into sin and debt.)

(al-Bukhaari, 833; Muslim, 588). Then after that he may make du’aa’ as he likes, asking for good in this world and in the Hereafter. And if he recites some of the du’aa’s narrated in the Sunnah, that is better. See question no. 5236.

 And Allaah knows best. May Allaah send blessings upon our Prophet Muhammad.