If you want to increase width of column widths for a SharePoint list, add a Content Editor WebPart to the list view and add following css code to the inner Html.
<style type="text/css">
.ms-vh-div[DisplayName='Title']
{
width:200px;
}
.ms-vh-div[DisplayName='Description']
{
width:300px;
}
.ms-vh-div[DisplayName='Category']
{
width:100px;
}
.ms-vh-div[DisplayName='Priority']
{
width:60px;
}
</style>
