In Drupal 7 the theme and template layer can easily be over complicated, but this is the quickest and most effective way in my opinion to get started using template files in your custom modules. Get in the habit of using a template file instead of putting pieces of HTML inside your module code. This system is pretty flexible and you can create a template for a small item or for a whole page.
Event tracking with Google Analytics has pretty much become a standard on all new sites. Google provides ample documentation on using the analytics, but the tricky part is getting it to integrate the way you want with Drupal. The Drupal Google Analytics module offers basic functionality out of the box. It can track page hits, specific user roles, offsite links, and download clicks. It also supports custom variables using tokens.
These 16 recommended Drupal modules are not all recommended for every project, but they among the more useful modules out there. Many of them are useful only for site developers.
Admin Menu - An improved admin toolbar with drop down menus.
Backup Migrate - A must have for importing/exporting Drupal databases. Conveniently omits the data from the cache tables. Admins can schedule regular backups on a timed basis.
There are many PHP frameworks out there, but 2 of my personal favorites are Drupal and CakePHP. WordPress is another popular in the world, and I have done many projects with it. I will say that WordPress has great documentation and a clean API, but it is rather limited in its capabilties. CakePHP and Drupal have proven to be flexible, scalable, and perfect for certain uses. The bottom line in this debate is that both are great, and both serve their purposes. Between CakePHP and Drupal, I feel a project of any size can be accomplished.
There is a veil of mystery surrounding SEO tactics. There are many modules out there that aid in improving your site's exposure. The easiest path for a beginning is to use SEO Tools. It basically gives you a list of prerequesites, and gives you some easy out of the box SEO.
Google Code Prettify is great for turning <code> tags into nicely formatted HTML. I personally appreciate how it displays the line numbers, but they don't get included when you copy+paste. There are many themes available but my favorite is the google code. It treats word wrapping well with line numbers, shows each line number, and is styled nicely. The Drupal module allows you to integrate it easily to Drupal.
Drupal Pretiffy module: http://drupal.org/project/prettify
Manually alter the Drupal theme in MySQL using these commands.
UPDATE system SET status=1 WHERE name = 'garland';
UPDATE variable SET value='s:7:"garland"' WHERE name = 'theme_default';
NOTE: There are many cache tables in Drupal 7 that may need to be flushed.