How should a Christian form, or respond to, political opinions? Here are a series of steps and standards, based on Biblical principles.
1. Commit to surrendering every political opinion to the Holy Scripture, and to test every political philosophy by the same standard. Paul is 2 Corinthians 9 said that it was his goal as a minister to bring every idea into obedience to Christ, no matter what that idea might be. Scripture holds highest authority over every idea, every principle, every philosophy. It is a sin to subordinate Scripture to worldly ideas. Paul also said in Colossians to beware world philosophies, out of which most political opinions form.
2. This requires a good working knowledge of both Testaments -- not just the New Testament. The Old Testament has a lot to say about nations, governments, civic ethics, and law. Every Christian should work on becoming Biblically literate. Read through the whole Bible once a year. Attend quality Bible studies. Read trustworthy material on the Bible. Attend a church where the pastor preaches the Bible in a literal, historical, and contextual way. You don't need to become a professional Bible teacher to know the Bible.
3. Do not adopt a worldly philosophy of politics, then artificially attach out-of-context Bible verses to its different points. God did not give us His Word to endorse world political philosophy. He expects us to use His word to form and follow a thoroughly Christian way of life, one that can stand on its own two feet. Nearly every world philosophy has some kernels of truths contained within it, some veins of truth running through it, but all world systems are riddled with serious errors.
4. Contemporary liberalism is built on a foundation of atheism, or agnosticism, Darwinism, and statism (the concentration of power into the hands of a centralized government). This makes liberalism essentially anti-Christian. Liberalism sometimes overlaps with the Bible in areas such as justice for the poor, but it approaches those issues from a radically anti-Christian starting-point. Liberalism is humanistic, and as humanism it has historically been promoted as a alternative to Christianity's influence.
Conservatism, on the other hand, has a history in the Western world (especially in England) of being influenced by Christianity, which has exerted a positive effect upon it. America's founders drew upon the Bible as they formulated the new nation. British conservatism gave us the Constitution, and anti-monarchism. But secular conservatism is also based on tradition, experience, and unredeemed human reasoning. Scripture is merely one source among many, not the highest rule of all philosophical truth.
There is also a breed of conservatism which is just asDarwinistic and humanistic, in its own way, as liberalism is; such as a certain kind of conservatism which denies the sinfulness of the human race. Both systems are infected by moral pragmatism -- the devilish doctrine that the ends justify the means.
My bottom line is, don't jump on this world's political band-wagons, no matter where you live! We Christians are citizens of the kingdom of God first, and citizens of particular nations after that. The Bible speaks authoritatively to matters of economics, courts, war, and the law, just as it speaks to relationships, the heart, and personal salvation. Keep a sanctified mind regarding the politics of this evil age, and guard your heart, for out of the heart flow all the rivers of life.