I feel ridiculously dumb to admit this but I didn't know for a while that System.Windows.Forms.Form implements IDisposable. So I managed to spend a few years writing code that created and displayed forms that were never disposed. This obviously created some memory leaks in my apps... *face palm*

If you are displaying a form once then moving on, wrap your form reference in a using statement.

using(MySuperForm myForm = new MySuperForm())
{
  dmyForm.ShowDialog();
}

If a using statement isn't appropriate, have your class implement IDisposable and clean up after itself.

public class MySuperClass : IDisposable
{
  private MySuperForm _myForm;
  
  public void Dispose()
  {
    if(_myForm != null)
      _myForm.Dispose();
  }
}