Fieldsets are a good way to group form items that naturally go together. Likely candidates for grouping are personal info (name, address, phone, etc.), credit card information or checklists, like the example below.
Here's the HTML for the fieldset above.
<form method="post">
<fieldset>
<legend>Choose your favorite campus icon</legend>
<input id="campanile" name="icon" type="checkbox" />
<label for="campanile">Campanile</label>
<input id="laverne" name="icon" type="checkbox" />
<label for="laverne">Lake LaVerne</label>
<input id="seasons" name="icon" type="checkbox"/>
<label for="seasons">Four Seasons fountain</label>
</fieldset>
</form>
