The Conditions of the Shahadah
Pronouncing the testimony of faith is sufficient to make one a convert to Islam. There are however, seven conditions that must be observed before it can effectively make one a Muslim. These are describe as follows:
1 Knowledge (Al-ilm)
Knowledge (al-ilm) of its meaning, what it negates and affirms. If a person says it without knowing its meaning, nor what its requirements are, then he will not benefit by it, because he has not believed in what it requires. Rather, he is like someone who speaks in a language that he does not understand.
The heart must be firmly certain of the meaning of Shahadah without a blemish of doubt.
Allah the Exalted says:" Verily, the believers are only those who truly believe in Allah and His Messenger, and then doubt not. (Quran 49:15).
The Messenger of Allah, peace be upon him, said: "I bear witness that there is no god but Allah, and I am the Messenger of Allah. No slave meets Allah with this testimony, having no doubt in it but shall enter Jannah."( Muslim) :
Exclusively worshiping Allah, which is contrary to shirk. This is what laa ilaaha illallaah points towards.
Allah, the Exalted, said:" And they were not commanded but to worship Allah, being sincere in devoting religion to Him." (Quran 98:5).
Abu Hurairah said:" I asked the Messenger of Allah, peace be upon him: Messenger of Allah! Who will be most fortunate to enjoy your shafa'ah (intercession) on the Day of Resurrection? The Messenger of Allah, peace be upon him, said: I was certain that no one else would ask me about this other than you, because I have noticed your keenness for hadeeth. The most fortunate of men who will enjoy my shafa'ah on the Day of Resurrection is the one who says: (La Ilaha Illa Allah) "None has the right to be worshiped except Allah", sincerely from his heart.."(Musnad al-Imam Ahmad.)
Truthfulness (as-sidq), which prevents hypocrisy (nifaaq). Indeed, the hypocrites uttered it with their tongues, but did not inwardly believe in what it signified.
The Messenger of Allah said: "Anyone testifies that there is no god but Allah and Muhammad is the Messenger of Allah, truthfully from his heart, Allah would forbid his admittance to the Fire."(Muslim)
5 Love and affection (Al-Mahabbah )
Love (al-mahabbah) for this kalimah and having love and pleasure for whatever it necessitates. This is contrary to the [state of the] hypocrites.
The Messenger of Allah, peace be upon him, said: "There are three (qualities), whoever possesses them, will taste the sweetness of Iman (belief): to love Allah and His Messenger more than anyone else, to love the Muslim only for the sake of Allah, and to dread returning to kufr (apostasy) as he dreads being thrown in fire." ( Bukhari and Muslim.)
Allah says to His Messenger (peace be upon him)
Say (O Muhammad SAW to mankind): "If you (really) love Allah then follow me (i.e. accept Islamic Monotheism, follow the Quran and the Sunnah), Allah will love you and forgive you of your sins. And Allah is Oft-Forgiving, Most Merciful." (3:31)
Allah says: "Allah shall bring forth a people whom He loves and they love Him." (Quran 5:54)
The Prophet, peace be upon him, also said: "None of you shall (really) believe until I become dearer to him than his own father, and son and all mankind." ( Bukhari and Muslim.)
6 Submission (Al-Inqiyaad) internally and externally
Submissive compliance (al-inqiyaad), by fulfilling its rights - which are the obligatory actions - with sincerity to Allah and seeking His good pleasure. This is its requirement.
Allah, the Exalted, says: "And he who submits himself to Allah, and does good, he has surely grasped a strong handle." ( Quran 31:22).
Allah also says:" And turn you to your Rabb, and submit yourselves to Him."

Quran 39:54).
7 Acceptance and conformity (Al-Qubool )
Acceptance (al-qabool), which prevents rejection.
This is achieved by acting upon what Allah has commanded and abandoning whatever He has prohibited.
read more here:
http://www.muslimconverts.com/shahadah/converting.htm