String localization guidelines

1. Use woocommerce textdomain in all strings.
2. When using dynamic strings in printf/sprintf, if you are replacing > 1 string use numbered args. e.g. Test %s string %s. would be Test %1$s string %2$s.
3. Use sentence case. e.g. Some Thing should be Some thing.
4. Avoid HTML. If needed, insert the HTML using sprintf.

For more information, see WP core document i18n for WordPress Developers.