Khan Academy is a great place to start. I second that recommendation. Although I was pretty confident in my maths up through basic calculus, I began fresh earl

Khan Academy is a great place to start. I second that recommendation. Although I was pretty confident in my maths up through basic calculus, I began fresh earlier this year starting from pre-algebra on their videos and problem sets. I took the approach of looking at the mind as a muscle and if I had taken a long break from lifting, I wouldn't jump right back in lifting the same weights. The analogy isn't perfect, but I feel like it helped to reinforce the old basic neural pathways in order to prime my mind for more difficult topics. EDIT: Also the achievement points aspect helped as a learning tool as well.