There are a number of different levels on which we have to push back:
1). The most important thing for us to do is to begin with ourselves, and to make sure that we are living a pious Christian life, in accordance with the Orthodox Tradition. If we do so, we will influence those around us, and what we say and do otherwise to defend traditional values will carry weight, whereas if we speak out about these values, but do not live them ourselves, everything else we say and do will be a waste of time.
2). Going one step further, we must make sure that our homes reflect traditional Orthodox Christian values. Aside from working on ourselves, ensuring that our children will grow up to be devote Orthodox Christians is the greatest work we can accomplish.
3).We should also work within our parish to make sure that there is one more welcoming spiritual haven for those seeking salvation. A parish has many things that need to be done, and not everyone can do them all, but everyone can do something. We should ask God to show us what our part is, and take it as seriously as we would our secular jobs… in fact we should take it more seriously.
4). Beyond that, there are a number of things that we can do impact those outside of our parishes:
a). We can of course pray for our country and for the whole world. This is a very important duty that we all have.
b). Since we live in a representative democracy, we can and should vote for candidates that reflect Christian values. We never have perfect choices, but we should pray, and vote for those who come closest to the values that we hold. Among the highest values that we hold are the sanctity of human life and the sanctity of the family. We should not vote for those who favor killing innocent unborn children for the sake of convenience. We should also not vote for those candidates that seek to undermine the traditional definition of marriage, or support other policies that are detrimental to the family. Sometimes weighing these values and looking at the choices we have can be difficult, and of course reasonable Christians can disagree, but let everyone vote their conscience first — not their pocketbook.
c). We can make sure that we are well informed, so that we can talk intelligently with our friends and coworkers about these issues, and hopefully sway them over time.
d). Some may be called to run for public office themselves, and there is no reason why a pious Orthodox layman should not pursue so a path, if they feel that this is what God has for them to do.
e). You can support groups that defend Tradition values with your time and/or your money. You can also engage in lawful protests.
f). And if it should come to the point that the government is either asking us to do things that we cannot in good conscience do, or forbids us from doing things that our conscience requires us to do, we can engage in civil disobedience.
I would encourage you to read The Basis of the Social Concept of the Russian Orthodox Church, especially the section on the relationship between Church and State, Christian Ethics and Secular Law, and the section on the Church and Politics.