WordPress is an amazing tool and of the Content Management Systems I have used, it is by far the most SEO Friendly out of the box. However, there are still issues with pages on your site straight out of the box. A lot of the pages on your blog can cause duplicate content issues. However, straight out of the box this isn't an issue. Your blog will still rank for all your keywords and there is no danger of your blog – which is full of unique content – from being deindexed. Not actioning the duplicate content issues on the pages I've detailed below won't harm your site.
However, if you make changes to your site detailed below, you'll find more of your site will be indexed in search engines. More of your site indexed in search engines means more long tail phrases will rank highly in search engines, which should give your more traffic.
Monthly/Yearly Archive Pages
Okay, this is a bit of a lie here. Archives of months and years, whilst important, hold no easily changed SEO value. They are simply archive pages that hold very little SEO value. So you're best off disabling them.
This is easily done though in WordPress using Yoast's WordPress SEO. After installing the plugin (if you don't already have it, which you should), go to the SEO > Indexation page in the WordPress Administration and tick the boxes next to “Subpages of archives and taxonomies” and “Date-based archives”. This will prevent search engines from indexing the pages:-
(The other boxes I'd recommend unticking, for reasons I'll highlight below)
Note: These pages will still be crawled by search engines, so any links will still pass juice, just that the pages won't be in the search engines. This is important as you want to highlight your best and most relevant pages. Your archives are likely less relevant than individual posts.
Tag Pages
Tag pages can be a great source for long tail traffic. But you need to treat them with respect.
First of all, you need a structure for the tags. You shouldn't call tags the same as your categories. Furthermore, you should try to limit tags as much as possible (so don't have a separate “SEO” and “Search Engine Optimization” tag). Furthermore, you need to push your tag pages. They are automatically linked but need some content on them. If you introduce tags using the description (a paragraph or two will suffice), then you can turn your tag pages into effective landing pages by adding a couple of lines of code to your tag.php template file (I have written about how to add tag descriptions to your tag.php file here).
I also use the plugin Tag Images to add images to the page, making it more user friendly. An example of this is on one of my blogs, which has a Chester FC landing page.
Author Pages
Rich Author pages are going to be vital for your blog in the next few years. By creating a rich author page, with an author bio, links to social networks and other websites that the author helps run, you can rank for the author's name. This could lead to an influx of traffic when – say – an author of your blog gets a bit of coverage in the major press.
Furthermore, with effective implementation of rich snippets, and you have authoritive guest bloggers on your site, you can increase clickthroughs to your site by having familiar avatars appear in the Search Engines by your link. Here's an example of one of my posts on Famous Bloggers:-
Implementing rich snippets is fairly straightforward with a tool such as Author Plus, though it does take time for Google to show them in the search engines.
However basic implementation can be done fairly easily using your current author bio (the one shown at the end of posts) – a tutorial is available here. This will give you rich author pages such as the ones seen on this very blog.
In Conclusion
None of the above is mandatory for your blog, your site won't drop from search engines because you fail to do the above. However, if you want to make your site get more traffic from search engines, by optimizing less obvious pages, you will give yourself a competitive advantage over other bloggers in the search engines.