For learning Wordpress, I found it best to grab a few templates (lots of free ones out there) and see how they work. Very quickly you see the basic tricks.
For plug-ins, go to the standard plugin site and go through all of the "popular plugins." There's a zillion, but you'll probably have 10-15 installed before you're done, so it's worth pawing through them. Maybe decide to add one a day.
There's also the curated plugins that WPEngine has. (Fair warning: I'm a co-founder.)
For more specific reference, these are the plugins I use (yes, actually USE) on my blog:
- Akimet (spam protection -- MUST have this; bots are crazy)
- CommentLuv (auto-adds links to latest post from your commentors -- a way to thank and promote people who comment)
- Get Recent Comments (sidebar of latest comments, again to thank/promote)
- Comment Relish (auto-email person first time commented to thank them etc. -- people write me back a lot of times resulting in a tighter bond)
- Google XML Sitemaps (creates proper Google sitemap automatically)
- No Revisions (Wordpress saves a post revision every time you hit "save." Yes you can revert but this fills your database with crap which slows down the database.)
- Robots Meta (automatically create a "robots" meta-tag so search engines strobe your site correctly)
- Secure WordPress (alerts you to common insecurities -- Wordpress is easily hacked!)
- WP-phpMyAdmin (puts phpmyadmin inside wordpress - just convenient if you like to look inside MySQL)
- WP Greet Box (messages like "hello digg user!" customized to source URL encouraging them to subscribe or whatever you want to say)
- WP Super Cache (automatically caches plain-HTML versions of your pages so when you get slammed by Hackernews your Apache doesn't crater. This saved me completely!!)
- Yet Another Related Posts Plugin (adds "related posts" at the end of posts -- people really do click those and it's great for new subscribers who haven't seen your old stuff. This plug-in does a good job scoring what "related" means.)
Final caveat -- You'll notice these on my blog, plus things like the "Tweet this" magic button. Most of these I've un-hooked from their standard installation and re-hooked using my own custom PHP, so that's why some of it will act/look differently on your site.
That's just the cost of getting things JUST the way you want. But out of the box all these plug-ins are good.