After searching for hours in google and stackoverflow, I did not get the answer for good practices for AngularJS.
My Questions Are ::
1) Is it a good practice to manipulate a DOM using JQuery and CSS in AngularJS?
2) When to add $injector and $inject explicitly?
3) Is it good practice to use JQuery's $.ajax() method to call the asynchronously in the controller of a Module?
1) Is it a good practice to manipulate a DOM using JQuery and CSS in AngularJS?
You may be surprised how much Angular can do without jQuery. However, jqLite is certainly a "lite" version of jQuery. If you can't do it "clean" in Angular (e.g., if you find yourself writing parent().parent() instead of closest('.element-wrapper')) then sure, reach for jQuery.
2) When to add $injector and $inject explicitly?
Normal dependency injection is usually sufficient. You could, however, dynamically inject a service using the $injector, if you really need to: AngularJS dynamically inject scope or controller
3) Is it good practice to use JQuery's $.ajax() method to call the asynchronously in the controller of a Module?
Use $http or $resource. They do things $.ajax() doesn't, e.g., they'll initiate an AngularJS digest cycle when results come back from the server. Often, you'll want to put your server interaction code into an Angular service.