Can we make du`a to Allah for UN important things ?

I have always wondered if it was ok make dua to Allah for things that are not very important ? I mean mostly we make dua for health or to find solutions to our problems, jobs/studies etc. But imagine for example I'm going to play some sport or anything like that can I ask Allah that I win ? etc. Do you see what I mean? I've always though there were things that were not worthy enough of asking Allah...

As’salaamu Alaikum,
Yes, I understand what you mean sister/brother! ^-^
As per The Noble Qur’an:

"O mankind! It is you who stand in need of Allah, but Allah is Rich (Free of all wants and needs), Worthy of All Praise."
—35:15

And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided.
— 2:186

So remember Me; I will remember you. And be grateful to Me and do not deny Me. O you who have believed, seek help through patience and prayer. Indeed, Allah is with the patient.
— 2:152-153

As per the Hadith of the Prophet (SalAllahu Alaihi wasallam):

"If one does not ask Allah, He will get angry with him." [Sahih al-Jami` no.2414]
"Nothing is more honourable to Allah the Most High than du`a." [Sahih al-Jami` no.5268]
“The most incapable person is the one who does not make du`a, and the most miserly person is the one who does not give salaam.” [Sahih Al-Jami` no. 1055]

And I believe this last Hadith will help answer your question, insha’Allah:

“Ask Allah for everything, even the lace of your shoes. If Allah does not provide, it will never be available." [Ibn al-Sunni, no. 349 - hasan. Supported by at-Tirmidhi 4/298 and others.]

I hope that helps insha’Allah! May Allah (SWT) bless you and your family, Ameen! :)