How to Preview ePub.
ePub preview should be performed both on computer and on major real devices. To preview on computer you need to install at least one ADE based ePub reader. Other readers based on browsers are not recommended, such as Calibre, because broswer based reader can not reveal the problems on real devices. The meaning of preview on computer is just to catch those problems before tranferring to real devices.
Install a previewer
You can install either of the three major previewers on PC,
Either one of them is OK for the testing work, you can install all of them of any one of them. They all bases Adobe SDK, the same base of most e-ink eReaders, and performs alike.
Associate ePub file
But ADE has an advantage, *.epub can be associated with ADE, so that when you double click on an epub file, ADE will be invoked automatically, that's very convenient for ePub Maker users when they made an epub then preview it by just clicking the file link in ePub Maker.
Previewer can be used before real test on real device, but test on real device can not be omitted. And there's no proper previewer for iPad on PC, and iBooks has a different epub standard, you may have to test on iPad.
Preview On Real Devices
There are too many different devices on market, from dedicate reader to tablet, to mobile phones. We can not test on most or even part of them. So we have to do the test smartly, we should
Preview on several major devices that has most market share.
Preview on a major device of a system, such as Nook or Kobo for all e-ink devices(Adobe system) and preview on iPad for all Apple devices.