Okay, so I'm assuming you have these custom fields posted on the thread page itself and now you want them listed on the thread list on each individual forum page. Luckily, there's a fairly simply method for accomplishing this. What you need to do is open the thread_list_macros template.
Inside that template, you'll need to search for the place you want this custom field text to be placed. In the past, when I've done this sort of thing, I added the text after date that sits below the title. Search for this line (in version 2.2.2):
<li class="structItem-startDate"><a href="{{ link('threads', $thread) }}" rel="nofollow"><xf:date time="{$thread.post_date}" /></a></li>
Then, after that line, you'll want to add your custom code. Let's say that you have custom thread fields for city, state, and zip code. Let's pretend that these Field ID names for these are LocationCity, LocationState, and LocationZip respectively. The code you would add right after that line above is:
<!-- ADD CUSTOM FIELDS -->
<xf:if is="{$thread.custom_fields.City}"><span>·</span> {$thread.custom_fields.LocationCity},</xf:if>
<xf:if is="{$thread.custom_fields.LocationState}">{$thread.custom_fields.LocationState}</xf:if>
<xf:if is="{$thread.custom_fields.LocationZip}">{$thread.custom_fields.LocationZip}</xf:if>
<!-- ADD CUSTOM FIELDS -->
I added a few more things to this as well, such as comments and a bullet point before the first custom field. Give this a try and let me know how that works.