Integrate Pagination Plugins into Twenty Twelve

The ‘next/prev’ posts links are done with a function in Twenty Twelve; twentytwelve_content_nav().

That function is pluggable, which makes it easy to change it in a child theme of Twenty Twelve.
To integrate for instance the plugin ‘wp_pagenavi’, you would need to change the function as follows (when you are using a child theme, add this into functions.php of the child theme; else edit the function in Twenty Twelve):

function twentytwelve_content_nav( $html_id ) {
	global $wp_query;

	$html_id = esc_attr( $html_id );

	if ( $wp_query->max_num_pages > 1 ) : ?>
		<nav id="<?php echo $html_id; ?>" class="navigation" role="navigation">
			<h3 class="assistive-text"><?php _e( 'Post navigation', 'twentytwelve' ); ?></h3>
		<?php if( function_exists( 'wp_pagenavi' ) ) { wp_pagenavi(); } else { ?>	
			<div class="nav-previous"><?php next_posts_link( __( '<span class="meta-nav">&larr;</span> Older posts', 'twentytwelve' ) ); ?></div>
			<div class="nav-next"><?php previous_posts_link( __( 'Newer posts <span class="meta-nav">&rarr;</span>', 'twentytwelve' ) ); ?></div>
		<?php } ?>
		</nav><!-- #<?php echo $html_id; ?> .navigation -->
	<?php endif;
}

the use of the conditional check if( function_exists( 'wp_pagenavi' ) ) prevents an error message if the plugin is not activated, and provides the theme’s default pagination as a fallback.

Posts in Two Or Three Columns – Twenty Twelve

If your index and archive pages are getting too long, or if you want to compact the information within those pages a little bit, for instance because the featured images above each post are just too large, consider to change the template to show the posts in two columns.

This is easier done than said, with some useful css classes injected into the output of the ‘post_class()’ in the div of each post, together with some rather simple css.

For instance, to change the category archive into two columns, without editing category.php itself, add a filter function into functions.php (as always with the default themes of WordPress, this  is done within a child theme):

add_filter('post_class','category_two_column_classes');

function category_two_column_classes( $classes ) {
global $wp_query;
if( is_category() ) :
$classes[] = 'two-column-post';
if( $wp_query->current_post%2 == 0 ) $classes[] = 'two-column-post-left';
endif;
return $classes;
}

The minimum css for this is:

.two-column-post { width: 47%; float: left; margin-left: 5.9%; }
.two-column-post-left { clear: left; margin-left: 0; }

If you want to apply the same principle for instance to the posts page or other archives, replace

is_category()

with another conditional tag like

is_home()

.
The code is easily adapted to three columns (or actually any number of columns) by changing the number in the modulus operator:

add_filter('post_class','category_three_column_classes');

function category_three_column_classes( $classes ) {
global $wp_query;
if( is_category() ) :
$classes[] = 'three-column-post';
if( $wp_query->current_post%3 == 0 ) $classes[] = 'column-post-left';
endif;
return $classes;
}

the css for three columns would be:

.three-column-post { width: 30%; float: left; margin-left: 4.9%; }
.column-post-left { clear: left; margin-left: 0; }

Sidebar on the Left – Twenty Twelve

A quick fix to move the sidebar location in a child theme of Twenty Twelve;

add these styles to style.css of the child theme:

@import url('../twentytwelve/style.css');

/*-- move sidebar to the left --*/
@media screen and (min-width: 600px) {
	.site-content {
		float: right;
	}
	.widget-area {
		float: left;
	}
}

/* for IE8 and IE7 ----------------*/
.ie .site-content {
	float: right;
}
.ie .widget-area {
	float: left;
}

caveat: this simplified set of styles has some problems with the formatting of the widgets in the ‘front-page’ template, when viewed in older browsers such as IE7.

possible helpful styles:

.ie .template-front-page #secondary.widget-area { width: 100%; }
.ie .template-front-page #secondary.widget-area .first.front-widgets { width: 50.1%; margin-right: 3%; background: #f4f4f4; }
.ie .template-front-page #secondary.widget-area .second.front-widgets { width: 46.8%; margin-right: 0; background: #f4f4f4; }
.ie .template-front-page #secondary.widget-area .widget { width: 100%; }