Consider retaining a US Patent Attorney
Filing a US patent application can be a complicated process. Foreign Applications can become even more complicated especially when claiming priority to an earlier filed application. If you have any thoughts on filing foreign you should consult a US patent attorney right away. Eventually, you will need to retain foreign counsel. Typically US attorneys will have relationships with the foreign associates and will be able to guide you to a trustworthy foreign associate. If you choose to proceed without a US Patent Attorney you will need to carefully research to foreign associates.
Determine if you have any public disclosures prior to a filing date in any country
Most foreign countries require absolute novelty to obtain a patent. This means that you cannot have a public disclosure prior to a filing date in any country. If you filed a US application prior to disclosing the invention to anybody then you can claim priority to that date if you file foreign applications within twelve months of the first filing date. The best practice is to file right away before any disclosures. Short of that you might be able to use confidentiality agreements to avoid any disclosure from becoming public.
Determine which countries you want to file foreign applications in.
Foreign filings can become very expensive very quickly. Filing in multiple countries can be very expensive because expense is added for every country. If you are filing in multiple countries or don't know which countries you want protection in you may want to file a Patent Cooperation Treaty Application which will allow you to delay your decisions up to 30 months from your earliest filed application. If you are only filing in one or two countries you may want to file directly in those countries.
Decide on which type of application to file and contact your US patent lawyer
Once you have made the decision on which type of foreign application to file you should contact your US lawyer and tell them if you want to file a PCT or direct applications. If you have already filed a US case you should tell the US Patent Attorney as soon as possible after the US filing. The foreign application should be filed within 12 months of the first filed application. The US Patent Attorney will then take the proper steps to have the application(s) filed.