<ul id="ex">
<li class="one">class="one"</li>
<li class="two">class="one two"</li>
<li class="three">class="three"</li>
<li class="one">class="one"</li>
<li class="two">class="two"</li>
<li class="three">class="three"</li>
<li class="one">class="one"</li>
<li class="two">class="two"</li>
<li class="three"><strong>class="three"</strong></li>
</ul>
$(function(){
$('#ex').find('li').each(function(){
if ($(this).is('.one')){
$(this).css({'color':'#f00'});
}else if($(this).is('.two')){
$(this).css({'font-size':'30px'});
}else if($(this).is(':has(strong)')){
$(this).css({'font-size':'50px'});
}
});
});