How to sue someone in another state? for small claims

If you mean NY Small Claims Court you can't because in order to have personal jurisdiction the defendant must either reside or work in the County where the court is.

I am not licensed to practice in NY, so I am going to give general info: Most states have VERY specific criteria in order to file a Small Claims Case. This includes suing a defendant that is out of the area, or even the state. In CA, the only way to sue a foreign (out of the State) defendant in Small Claims, is if it is the result of an auto accident OR if the foreign defendant own real property in CA and the claim relates to that property. The only way, which can be objectionable, is if the "injury" occurred in CA AND the defendant is in CA when served. Otherwise, the case is not permitted to proceed. I do not know what to expect for NY, so I would consult with a local attorney. Further, just because you CAN go to Small Claims, does not necessarily mean you should. Speak with a lawyer to see if it is worthwhile suing in the Supreme Court in order to sue the foreign defendant.