By Images_of_Money's profile - www.flickr.com, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=19145960 With UK self-assessment tax return forms due with HMRC by January 31st, Jonathan Amponsah of The Tax Guys gives his advice on mistakes you can avoid when filling one in  Filling out a personal tax return can be stressful. It's surprising given it's a…