I'm so glad you asked because Romans 14 has a magnificent answer to your question!
We remember from a few posts ago that to eat with offense is sin, or rather to violate your extra-moral standards is a sinful act. But why exactly? Looking at Paul's explanation, we find a simple process by which we must make our decisions. In Romans 14:20-23, the Bible proclaims,
"For meat destroy not the work of God. All things indeed are pure; but it is evil for that man who eateth with offence. It is good neither to eat flesh, nor to drink wine, nor any thing whereby thy brother stumbleth, or is offended, or is made weak. Hast thou faith? have it to thyself before God. Happy is he that condemneth not himself in that thing which he alloweth. And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin"
Whatsoever is not of faith is sin. That is why it is so sinful for us to violate the standards that we have developed. But wait a minute! This means I'm assuming that faith is a part of the process of determining extra-moral standards.
Indeed, that is exactly what Paul is assuming here. It is not a question of anything else. "Whatsoever is not of faith is sin." If your standards for extra-moral concerns are not of faith, then all actions based upon them are sin.
This is how we must make our decisions - through prayer. By examining and studying the following verses (and many more), and praying about how those standards look in today's world:
"Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things." ~ Philippians 4:8
"Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days: Which are a shadow of things to come; but the body is of Christ. Let no man beguile you of your reward in a voluntary humility and worshipping of angels, intruding into those things which he hath not seen, vainly puffed up by his fleshly mind, And not holding the Head, from which all the body by joints and bands having nourishment ministered, and knit together, increaseth with the increase of God. Wherefore if ye be dead with Christ from the rudiments of the world, why, as though living in the world, are ye subject to ordinances, (Touch not; taste not; handle not; Which all are to perish with the using;) after the commandments and doctrines of men? Which things have indeed a shew of wisdom in will worship, and humility, and neglecting of the body: not in any honour to the satisfying of the flesh. If ye then be risen with Christ, seek those things which are above, where Christ sitteth on the right hand of God. Set your affection on things above, not on things on the earth." Colossians 2:16-3:2
"Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage. Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing. For I testify again to every man that is circumcised, that he is a debtor to do the whole law. Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace. For we through the Spirit wait for the hope of righteousness by faith. For in Jesus Christ neither circumcision availeth any thing, nor uncircumcision; but faith which worketh by love.For, brethren, ye have been called unto liberty; only use not liberty for an occasion to the flesh, but by love serve one another." ~Galatians 5:1-6, 13
And of course, many, many more.
The decision shouldn't just be made by convenience. It can't be, "I love Doctor Who, so it's definitely appropriate for me to watch!" All things need to be evaluated on the principles found in the Bible, and prayed about. You need to determine how x, y, and z will affect your relationship with the Lord and others.
It's a decision that needs to be taken by faith, and dare I say it, not because your church tells you to, nor because your friends tell you so, and to a degree, not because your parents have chosen this standard. Now on that last point, don't get me wrong, you should honor your parent's standards wholly in all things. But maybe you'll be led to hold yourself to a higher standard than they do. Or maybe when you're starting a family on your own, you should evaluate the standards you have in your life by faith and by prayer.
As Romans 14:5 says,
"One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind."