I spend a lot of time working with WordPress, using it for simple blogs and also as a CMS solution for client sites. Some of my most used code snippets and tricks I have listed below.
Get your blog URL

<?php bloginfo(’url’); ?>

Linking to an image/file (not from CSS file)
In this case you will need the URL [...]

Simple way to check if your WordPress post has an excerpt specified and either show the_excerpt or the_content.

!empty($post->post_excerpt)

Example:

<?php if (!empty($post->post_excerpt)) { ?>
<?php the_excerpt(); ?>
<?php } else { ?>
<?php the_content(’<p>Continue reading</p>’); } ?>