Below are few must use tips and libraries you would use for developing your phonegap mobile app.
CSS Box Sizing
Add below to your css file, its is very important for developing responsive apps.
*{
-webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */
-moz-box-sizing: border-box; /* Firefox, other Gecko */
box-sizing: border-box; /* Opera/IE 8+ */
}
A very good explation of box sizing property is given here http://css-tricks.com/box-sizing/
FastClick.js
This is a must have library, to improve speed of clicks and taps in your app. You can find more details here https://github.com/ftlabs/fastclick
FastClick is a simple, easy-to-use library for eliminating the 300ms delay between a physical tap and the firing of a click event on mobile browsers. The aim is to make your application feel less laggy and more responsive while avoiding any interference with your current logic.
iScroll.js
A very handy library for adding sliders, strollers, left scroll menu to your app. It has many uses and is a must have, download link https://github.com/cubiq/iscroll
Phonegap Plugins
Below are some of the must have phonegap plugins which every application uses
Google Analytics for your app:
https://github.com/phonegap-build/GAPlugin
Facebook Login for your app:
https://github.com/Wizcorp/phonegap-facebook-plugin
Native notifications for your app:
https://github.com/phonegap-build/PushPlugin
Save app preferences:
https://github.com/apla/me.apla.cordova.app-preferences
Share you app on social networks, whatsapp etc:
https://github.com/EddyVerbruggen/SocialSharing-PhoneGap-Plugin
Showing small alert/toast messages:
https://github.com/EddyVerbruggen/Toast-PhoneGap-Plugin
Find your app version, useful for feedback pages etc:
https://github.com/whiteoctober/cordova-plugin-app-version