Use the KISS (Keep It Simple, ...) principle for using transactions. You can follow the following guidelines, if you want to use transactions in your application.
Be consistent in usage of transactions. If you decide to use transactions in your application, do so in all the modules.
Turn off the AutoCommit flag as soon as the database connection is created.
Do not forget to use Rollback and Commit functions.
Do not use your understanding of Database specific transaction semantics.. like Oracle™s ability to commit selective SQL statements even when the transaction is on. This will surely hurt you in future, if you need to port your application to another database.