I am an Indian, working in the US on H1B visa. I want to apply for a Schengen visa for Italy after my marriage in India. I'll travel from US to India for marriage, will then fly from India to Italy and then from Italy back to the US. Therefore, I will apply for a Schengen visa while I am here in the US. I have a valid H1B till mid year 2018. Will there be any problem? What should be the course of application?
Your plan seems fine.
Will there be any problem?
From the information provided, there is no problem to be seen. It is of course possible that problems may arise because of circumstances you have not mentioned, or even circumstances of which you are unaware, so of course we cannot guarantee that there will be no problems whatsoever.
What should be the course of application?
First, you should identify which country is your main destination in the Schengen area. For example, if you are flying to Italy but spending most of your time in France, then France is probably your main destination.
Then you should identify which consulate is responsible for handling Schengen visa applications for the main destination country from your place of residence.
Then you should approach that consulate to find out how to apply for a visa. You can usually do this by finding the consulate's web site and following links for "consular services," "visa," "visit," or similar.