Paul's words to the Ephesians are what jump at me when I read what you asked.
Ephesians 6:10-13 - Finally, be strong in the Lord and in the strength of His might. Put on the full armor of God, so that you will be able to stand firm against the schemes of the devil. For our struggle is not against flesh and blood, but against the rulers, against the powers, against the world forces of this darkness, against the spiritual forces of wickedness in the heavenly places. Therefore, take up the full armor of God, so that you will be able to resist in the evil day, and having done everything, to stand firm.
Once we become a Christian, our primary job is to then spend the rest of our life growing in sanctification. Growing in sanctification simply means to become more like Christ. The more we become like Christ, the more we will love others, and the more God will be glorified and honored in and through us.
I think that the way we fight the good fight of faith is to seek to live a life that reflects the character of Christ.
Listen to Paul in his letter to Timothy: Fight the good fight of faith; take hold of the eternal life to which you were called, and you made the good confession in the presence of many witnesses. I charge you in the presence of God, who gives life to all things, and of Christ Jesus, who testified the good confession before Pontius Pilate, that you keep the commandment without stain or reproach until the appearing of our Lord Jesus Christ... Instruct those who are rich in this present world not to be conceited or to fix their hope on the uncertainty of riches, but on God, who richly supplies us with all things to enjoy. Instruct them to do good, to be rich in good works, to be generous and ready to share...O Timothy, guard what has been entrusted to you, avoiding worldly and empty chatter and the opposing arguments of what is falsely called "knowledge"— which some have professed and thus gone astray from the faith. Grace be with you.
