I am trying to skip certain nodes if a condition is met.

If the ad_content does NOT contain a label, I want to skip it.

> Is it best to do a "if test" like I did below, or is there a
> better technique that I need to learn?
...

I am sending this to a  template match. eg:
        <xsl:apply-templates select="ad/ad_content" />

Try
       <xsl:apply-templates select="ad/ad_content[label]" />
or
       <xsl:apply-templates select="ad/ad_content[normalize-space(label)]" />

HTH
J.Pietschmann