The single statement that is most useful to avoid bugs is Option Explicit. Always use it in every module of your applications. Even better, let the Visual Basic IDE automatically add one whenever you create a new module to your project. You can do it by selecting the “Require Variable Declarations” checkbox in the General tab of the Tools!Options dialog box.
Remember, however, that this option is only valid for modules that are created after you enforce it. If you import existing modules into your project, Visual Basic won’t automatically add Option Explicit for you. Therefore, a number of bugs may still occur.
Also be aware that many templates provided with VB6, most notably the modules in the DataProject template project, don’t include the Option Explicit directive.