Taking a default as plaintiff
You must submit proof of proper service, an affidavit establishing the defendant's failure to answer, and an affidavit of facts from someone with personal knowledge establishing the claim and the amount. In consumer credit matters, additional documentation requirements apply and courts scrutinize them closely. A thin submission gets denied, and repeated deficient applications waste months.
Don't let the default go stale
New York sets an outer limit on how long a plaintiff can wait before moving for a default. Blow through it and the court may dismiss the complaint as abandoned unless you show sufficient cause. Calendar the deadline the moment the defendant's answer date passes.
Vacating as defendant: excuse plus defense
The standard route requires a reasonable excuse for the default — never received the papers, illness, law-office failure, a genuine misunderstanding — plus an affidavit showing a defense with merit. Move promptly. Courts are far more receptive to a defendant who appears weeks after learning of the judgment than one who appears after a bank levy two years later.
The jurisdictional route
If you were never properly served, the court never obtained jurisdiction and the judgment is a nullity — no excuse analysis required in the same way. This is why service records matter so much. A traverse hearing, where the process server testifies about what they actually did, is the usual proving ground.