I have a request of God. I mean I have a wish that I want God accept. For many years I pray and asked God to accept it, but God doesn't accept my prayer. What should I do? What kind of prayer to God will be accepted?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Know, dear brother, when a slave supplicates Allah while fulfilling the conditions that are compulsory for the supplications to be answered and avoiding the hindrances that prevent the supplication from being answered, then Allah will surely respond to his supplications in this life, or He will reserve its reward for the next life, or He keeps the one who supplicates away from calamities.

Abu Sa’eed Al-Khudri narrated that the Prophet said: “If a Muslim makes Du'aa’ that does not contain any sin or severing kin relations, then Allah will surely grant him one of three things: either He gives him in this life what he had asked for, or he will reserve its reward for the next life, or He protects him from calamities due to his Du'aa’.” On hearing this, the Companions said: “Then we will supplicate too much.” The Prophet said: “Allah gives abundantly.” [Ahmad; Shu’ayb al-Arnaunt said: ‘The chain of this Hadeeth is Hasan (good)’]

Supplicating Allah attentively and strongly while believing that He will answer the supplications is one of the conditions for having the supplications answered. Abu Hurayrah narrated that the Prophet said: “Call upon Allah while being certain of being answered, and know that Allah does not respond to a supplication from the heart of one who is heedless and occupied by play.” [Ahmad, Al-Haakim, and At-Tirmithi]

Eating from lawful earnings and avoiding what is forbidden are also among the prerequisites for having one's supplications answered.
An important condition for the Du'aa’ to be answered is following Allah's Commands, abstaining from His Prohibitions, and strongly believing in His Promises.

Allah Says (what means): {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.} [Quran 2:186]

The hindrances that prevent the supplication from being answered are the Du'aa’ that contains sin or severing of kin relations or being impatient. Abu Hurayrah narrated that the Prophet said: “The supplication of the servant is granted if he does not supplicate for sin or for severing the ties of kinship (blood relations), or he does not become impatient. It was said: "Allah's Messenger, what does "become impatient imply? He said: “That he should say like this: I supplicated, and I supplicated, but I did not find it being responded to, and then he becomes frustrated and abandons supplication.”

In short, Allah will reward you in the next life for your supplications or He may protect you from evils due to your supplications, and sometimes Allah will delay answering your Du'aa’ for a wisdom He knows. So, you should not get impatient and should not give up making Du'aa’. On the other hand, you have only to fulfill the conditions we have mentioned above.

For more benefit on supplications, please refer to Fataawa 343300, 418060, 88282, 13277, 213715 and 377509.

Allah knows best.