The worship of a Muslim will not be accepted by Allah SWT, so there are two basic requirements in it. First, sincerely intend for Allah SWT alone. That is, the will of the servant in all his worship. Whether it is a word or a dzahir or inner act to seek the pleasure of Allah SWT alone. There is no hope of praise, praise, and material reps from other than Allah SWT.
Secondly, the worship is in accordance with the demands of the Shari'a that God desires. That is to follow the way of worship of Prophet Muhammad SAW. Do not stray the guidance of this Allah SWT. That worship is not the result of the creation of people; good shape, order, time, place, and so on.
Allah SWT says, "Whoever hopes for a meeting with his Lord should do good deeds and not associate anyone in worshiping his Lord." (QS Al-Kahf: 110)
That is to say, should be sincere for Allah and true in accordance with the Prophet's Salaah. Both are the fundamental principles of acceptance, sincere and true.
Ibn Katsir said in interpreting the verse, "(Whoever hopes for a meeting with his Lord), that is: reward and good reward from Him. (then let him do good deeds), meaning: the charity that is suitable for the law of Allah. (and he should not associate any person in worshiping his Lord), and that which is desired in charity is the face of Allah alone which has no associate with Him. "
He Rahimahullah went on to say, "Both of these are the fundamentals of charity received, that is to be the sincere sincerity for Allah, true to the law of the Prophet sallallaahu 'alaihi wasallam." (See Tafisr Al-Quran al-'Adzim, Ibnu Katsir in the commentary of the verse)
. . . should practice sincerely for Allah and true in accordance with the law of the Prophet sallallaahu 'alaihi wasallam.
Both are the fundamental deeds that are accepted, ie sincere and true. . .
Ibn al-Qayyim Rahimahullah in I'lam al-Muwaqi'in divided the slave charity into 4 parts. Of the four it was only one accepted, while the three were rejected. The charity accepted, according to him, is a charity that is done sincerely because of Allah SWT and according to the sunnah of the Prophet Muhammad. While the three who are denied is a charity that loses the two properties above or one of them.
Allah (SWT) says, "(Allah) Who created death and life, that He might test you, who among you is better in deed." (Surah Al-Mulk: 2)
Indeed the deeds of maqbul (accepted) are done sincerely and according to the sunnah. That charity is what is loved and blessed by Allah SWT.
Ibnul Qayyim rahimahullah once said, "do not act sincerely and follow the Sunnah like a traveler who fills the place of his drink with sand, very burdensome and does not give him the benefit." Wallahu A'lam.