Answer
Wa `alaykum as-Salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
We would like to make it clear that a Muslim has a firm belief that nothing happens in this universe except with Allah’s leave. No one can harm anybody or bring him benefit if Allah does not want this harm or benefit to occur. The Prophet (peace and blessings be upon him) instructed his cousin, `Abdullah ibn `Abbas, saying: “And bear in mind that if the whole nation is to gather to harm you, they will not be able to harm you except when Allah wills that harm to happen to you. And if all people are to gather themselves to benefit you, such a benefit will not occur if Allah’s will dictates otherwise.”
Regarding your question, we would like to furnish you with the fatwa issued by Sheikh Salih bin Fawzan Al-Fawzan, a prominent Muslim Saudi scholar:
There is no basis for the belief that eye twitching is a sign of bad omen in Islam. The Muslim has to put his trust in Allah.
Regarding things as bad omens is a kind of tiyarah (belief in evil omens), which the Prophet (peace and blessings be upon him) declared to be false and stated that it is a form of shirk (associating others with Allah).
If a person notices any such thing (ringing in the ears, twitching in the eye, etc.), he should ignore it and go ahead with his plans, and not hesitate. The Prophet (peace and blessings be upon him) said: “Tiyarah is that which makes you go ahead or refrain.”
A Muslim should also recite the following supplication: “Allahumma la ya’ti bil-hasanaat illa anta wa la yadfa` as-sayi’ati illa anta, wa laa hawla wa laa quwwata illa bik (O Allah, none can bring good things except You, and none can ward off evil things except You, and there is no power and no strength except with You).”
As for seeing something and interpreting it in an optimistic manner, this is good, and the Prophet (peace and blessings be upon him) used to like optimism. Optimism means thinking well of Allah.
Allah Almighty knows best.
Excerpted, with slight modifications, from: www.islamqa.info