How do you write step definitions that are reusable without becoming too generic or ambiguous?

Too specific — can't reuse:

When alice@example.com clicks the login button on page /login

The step is bound to one user, one URL, and one element — nothing else can reuse it.

Too generic — meaningless:

When the user performs an action

This conveys nothing about behaviour.

Right level of abstraction:

When the user logs in with valid credentials
When the user logs in with email {string} and password {string}

The first is reusable across happy-path scenarios. The second is parameterised for boundary/negative testing.

Parameterisation for reuse:

@When("the user submits the {string} form with {string}")
public void userSubmitsForm(String formName, String data) {
    formHelper.submit(formName, data);
}

Step definition organisation: Group step definitions by domain area, not by feature file:

stepdefs/
  AuthSteps.java        ← all login/logout/register steps
  OrderSteps.java       ← all order-related steps
  CommonSteps.java      ← navigation, generic assertions

The "one step definition, multiple features" test: If a step is referenced in only one feature file, it may be too specific. If it's referenced in 5+, check it's still specific enough to be meaningful.

Avoid "AND soup":

# BAD — 8 And steps doing unrelated things
When the user clicks and waits and scrolls and types and submits

Each compound action should be its own named step with a clear behaviour label.