Installing emacs packages (elpa) and also adding loading code to .emacs?

I've installed a few packages from elpa and melpa. Some packages don't really require that I edit my .emacs file to add any hooks or include a (require 'fn) line. On the other hand some packages provide instructions that explain editing the .emacs file is part of the installation. I recently installed ace-jump-mode and the packaging system created a directory for the package in .emacs.d something like: ace-jump-mode-20130719.2053/ and the instructions for installation call for adding a few lines to my .emacs file.

So there are 2 parts to this question.

1. when is editing .emacs file required after installing a package?
2. Adding that path to ace-jump seems like it will break if ever I need to update the package, is there a better way of including the path in my .emacs file?

1. Different packages handle key bindings and loading differently. Sometimes you'll have to modify your configuration, and sometimes you won't. The best bet is to read the documentation for each thing you install, which you appear to already be doing.

2. You shouldn't have to explicitly specify the path to your ace-jump package. ELPA / package.el will take care of updating your load-path. The following snippet should work, without specifying that path manually:

   ;; No (add-to-list 'load-path ...)
   (require 'ace-jump-mode)
   ;; Optional
   (define-key global-map (kbd "C-c SPC") 'ace-jump-mode)