An excerpt from http://www.sitepoint.com/ux-design-passwords-registration-forms/, by @kes
Forms are a crucial part of the web design in 2015, especially since the rise of mobile has forced us to concentrate that much harder on smoothing our user experiences.
They are central to driving conversions in ecommerce sites and good from design is often the difference between a successful user registration and losing them from the site permanently.
From a user perspective, forms need to clearly communicate to the user what is required from them. They should be effortless to click into and type in, regardless of the device that they're accessed on. And they should display with correctly aligned labels that indicate what the user needs to enter into a given field.
While it was once considered standard practice to ask for as much information as possible – on the off chance you may need this information later – that's not the case today. Forms should be not a character longer than is absolutely necessary.
Image credit: Will Scully-Power
Research has shown that shorter forms can increase conversions by as much as 160%, so a poorly designed form, or one that demands too much data can directly impact revenue.