It’s very common that you could get in trouble for duplicate content. I would highly recommend to not index your tags or categories as it would be duplicate content.
Simply place this in your header.php by simply going to Appearance > Editor > header.php. You will need to add this to the top.
<?php if(is_single() || is_page() || is_home()) { ?>
<meta name="googlebot" content="index,noarchive,follow,noodp" />
<meta name="robots" content="all,index,follow" />
<meta name="msnbot" content="all,index,follow" />
<?php } else { ?>
<meta name="googlebot" content="noindex,noarchive,follow,noodp" />
<meta name="robots" content="noindex,follow" />
<meta name="msnbot" content="noindex,follow" />
<?php }?>
This will make it so only your single posts, homepage and pages are the only pages that get indexed on your website.
If you prefer to install a wordpress plugin instead of adding it in directly you can checkout this plugin. WordPress › Robots Meta « WordPress Plugins
This plugin will do the exact thing above and a little more.
