Our conduct matters. To begin with, the effects of sin in our lives are taught in scripture.

1 Corinthians 11:30 (NIV):
That is why many among you are weak and sick, and a number of you have fallen asleep.

1 Peter 3:12:
For the eyes of the Lord are on the righteous and his ears are attentive to their prayer, but the face of the Lord is against those who do evil.

Psalm 19:14 (TLB):
May my spoken words and unspoken thoughts be pleasing even to you, O Lord my Rock and my Redeemer.

1 Peter 3:7 (AMP):
In the same way, you husbands, live with your wives in an understanding way [with great gentleness and tact, and with an intelligent regard for the marriage relationship], as with someone physically weaker, since she is a woman. Show her honor and respect as a fellow heir of the grace of life, so that your prayers will not be hindered or ineffective.

Psalms 66:18:
I had cherished iniquity in my heart, the Lord would not have listened.

Psalm 34:15:
The eyes of the LORD are on the righteous, and his ears are attentive to their cry;

James 5:16
The effective, fervent prayer of a righteous man avails much.

1 John 3:21-22 (AMP):
Beloved, if our heart does not convict us [of guilt], we have confidence [complete assurance and boldness] before God; and we receive from Him whatever we ask because we [carefully and consistently] keep His commandments and do the things that are pleasing in His sight [habitually seeking to follow His plan for us].

In summary, our conduct matters to God when it comes to Him hearing and answering prayer. Both the Old Testament and the New Testament say basically the same thing about this. The conduct of our lives literally affects the efficacy of our prayers.