Al-jawab billahi at-taufeeq (the answer with Allah's guidance)
Curing Wasawis (pl. of Waswasa):
Waswasa is from the Shaitan one should treat it with contempt and pay no attention to such thoughts and do not bother. If one gives a little attention to such thoughts, the Shaytan feels honoured. It has achieved its purpose of diverting one’s mind in wrong. One should never give into that. Simply treat such thoughts with contempt and ignore them.
Make a routine of reciting the Quran like morning and evening etc.
"We sent down in the Quran that which is a healing and a mercy to those who believe." (17:82)
Recite ‘Laa hawla walaa Quwwata Illaa Billaah’ abundantly.
Recite Istighfaar as much as possible.
Recite Ta’awudh (A’oodhu Billaah).
Recite La Ilaha IllAllahu Muhammadur Rasulullah.
Recite Surah Fatiha and Ayatul Kursi (2:255).
Recite the last verse of Surah Baqarah (2:285,286).
Recite Surah Yaseen in the morning.
Recite Muawwazatain (Surah Naas and Falaq) and Surah Ikhlas and blow over yourself from your nape to feet 3 times, after every Fardh Salah and before you retire to bed.
Remember, those who believe in Allah Ta'ala and His Messenger (Sallallahu Alaihi Wasallam) and obeys them, there shall be No fear on them, nor shall they grieve i.e. they will enter Jannat (Paradise).
Allah Ta'ala says,
"We said: "Get down all of you from this place (the Paradise), then whenever there comes to you Guidance from Me (i.e. Quran and the Messenger (Sallallahu Alaihi Wasallam)), and whoever follows My Guidance (believes in me and obeys me), there shall be no fear on them, nor shall they grieve (in the Hereafter, they will enter Paradise)." (2:38)
To increase one's Imaan one must be obedient to Allah and His Messenger (Sallallahu Alaihi Wasallam) and perform righteous deeds, this will lead to Allah Ta'ala and Jannat.
Please view this link on ways to increase Imaan and to gain closeness to Allah Ta'ala: http://www.muftisays.com/qa/question/1779/guidance.html
And Only Allah Ta'ala Knows Best.