I need advice in registering a company in USA as a non-resident.
Nearly any startup or corporate counsel worth their salt can give you advice on where to incorporate your company. In general it is most likely going to be Delaware but it truly depends on the scope, scale and nature of your operation. For example, if you want to import goods from another country and resell them in New York, it would save you a lot of time and headache to simply incorporate in New York than have to pay additional registration fees for each state jurisdiction. If, however, you are eventually going to be seeking investors for your company than a Delaware corporation is generally the standard formation filing for a startup seeking investors. It depends on what type of business you are looking to operate in the United States. Either way, best of luck.
Google law firms that register corps in Delaware, you'll find plenty
No one can give you legal advice who is not an attorney. There are a lot of services that advertise packaged assistance for incorporations, but many of them do not do any work to learn about your business or guide you on the best form of incorporation for your actual enterprise. Registering a company is different than incorporating your company. You can have a registered agent in the US and not be a US company.
From abroad one of the first question is usually something like, "Why do you feel you need to incorporate in the US?" And then things like determining where work actually occurs, where banking occurs, where taxes are paid, where employees are paid, what structure of ownership exists, what industry you're in, if any licenses are required, who is responsible for what in the company, and so on.
You can probably get basic advice from a consulate in your home country, about the ingredients that will go into doing international business between where you are and the United States, and if there are restrictions of which you should be aware. They can also probably offer suggestions on banks that handle international commerce with your country, and also on any reporting required for international business. It's a good place to start when you don't have any information at all.
The incorporation steps themselves are usually pretty easy, enough so that you can do them without help. But making sure you understand the implications of the decisions you make in setting up your company is far more complex and may benefit greatly from consulting with an attorney who understands commerce between the two specific countries. Again, the consulate can often point you to such resources.
Start with this link https://lk.usembassy.gov/business/ and go from there.
Hire a local attorney. It will probably cost $1500 - $2000. If you're in the Boston area I can recommend an excellent firm.