The most effective legal thing to do is boycott New York. Use them as a target for effect.
If only 25% of the populace that owned firearms would do this it might cause a state that can Ill afford more financial problems to notice.
If your considering a vacation, meeting etc. in New York change locations. Check any product your considering purchasing, if it's made in New York, look at one made somewhere else. Check where the ownership of any chain store or restaurant etc is. and if it's in New York look elsewhere.
Seems to be effective for most other groups of people.