The United Nations Convention on Contracts for the International Sale of Goods (CISG) automatically applies to many international sales contracts unless the parties opt out, and it fills gaps a short contract may not address explicitly. Beyond that, a contract should state which country's law governs it and how disputes will be resolved: through the courts of a named country, or through arbitration, which is often faster and more practical for cross-border disputes because the resulting award is easier to enforce internationally than a foreign court judgment.
For a small or first order, formal arbitration clauses may be impractical to negotiate, but you should still know, in principle, what your recourse would be if a serious dispute arose, rather than discovering you have none only after a problem occurs.