There are many options in the online store sales process, such as how (or if) you charge for shipping, whether it takes one or several screens to checkout, etc. etc.
The optimum process is not the same for all stores, it is going to depend on what you are selling, who you are selling to, and so on.
You can’t necessarily get the right answer to every question in advance.
Part of making an online store successful is testing. Plan on making changes and then seeing how that affects the visitor experience.
To evaluate this you have to have a good “web analytics” (stats) program.