What belongs to such prayer which is acceptable to God and which He will hear?

Heidelberg Catechism

Question 117. What belongs to such prayer which is acceptable to God and which He will hear?

Answer. First, that with our whole heart[1] we call only upon the one true God, who has revealed Himself to us in His Word,[2] for all that He has commanded us to ask of Him;[3]
second, that we thoroughly know our need and misery,[4] so as to humble ourselves in the presence of His divine majesty;[5] third, that we be firmly assured[6] that notwithstanding our unworthiness He will, for the sake of Christ our Lord, certainly hear our prayer,[7] as He has promised us in His Word.[8]

[1] Jn 4:22-24;
[2] Rom 8:26; 1 Jn 5:14;
[3] Ps 27:8;
[4] 2 Chron 20:12;
[5] Ps 2:10, 34:18; Isa 66:2;
[6] Rom 10:14; Jas 1:6;
[7] Dan 9:17-18; Jn 14:13-16;
[8] Ps 143:1; Mt 7:8; Lk 18:13