1. Stop Complaining! 1 Corinthians 10:10
It’s easy to complain, and while there are a few things that Christians can legitimately complain about, most of the complaining people do ought to be stopped.
1 Corinthians 10:10

2. We should not complain to God…
About suffering the consequences for our sins (Lamentations 3:38-39)
Because He extends grace to others (Matthew 20:11-12)
About the leadership He has ordained (Numbers 16)
About the blessings He provides (Numbers 11)
About having to keep His commands (Deuteronomy 1:26-27; Phil. 2:14-15)

3. We should also be cautious about complaining against our fellowman
There are beneficial complaints such as...
Complaints based on fact and aimed at gaining benefits for others (Acts 6:1)
Complaints that resolve sin (Colossians 3:13)
In general, we should avoid complaints against each others (James 5:9; Jude 16)