In one of my itemstyles I want the first element in the list to have a bit different look than the other items being displayed. How is it possible to take the first item?
Try following because *Main.xsl passes @order parameter to ItemStyle.xsl:
<xsl:if test="@Order = 1"> <!-- your logic --> </xsl:if>
This isn't really a SharePoint question but I think the answer you are looking for is something like this:
<xsl:if test="position() = 1"> <!-- do your custom formatting logic --> </xsl:if>