How to adjust / resize SharePoint 2013 List View columns?

You can change the width (or anything) using CSS.

<style type='text/css'>
.ms-vh-div[DisplayName='ColumnName']
{
  width:250px;
}
</style>

If you need to add this CSS to a page where you have multiple lists, you can target a specific list/webpart by using F12 Developer Tools to find the web-part ID and add it before .ms-vh-div.

#WebPartWPQX .ms-vh-div[DisplayName='ColumnName'] 

Where X is the number/ID of the webpart.