These books are focused on how well a person can use the interfaces you design.
Designing Interfaces: Patterns for Effective Interaction Design
This book collects up the common patterns seen in software design. Knowledge of design patterns is one of the best ways you can improve your ability to design good interfaces, because someone else has probably solved a similar problem before. If you know how they did it, you're already most of the way there.
Web Form Design: Filling in the Blanks
Forms are a big part of design - generally at some point you need to ask the user for some information. Luke is an expert on form design, and this book walks you through all of the principles you should keep in mind when you design forms.
Microinteractions: Designing with Details
Microinteractions are a little hard to define. They're the small moment-to-moment actions carried out by a user, and the software's response to them. They're also a big part of why interacting with software feels good or bad, so they're important to keep in mind.