Physics and Maths Tutor has always been incredible for me, practise past paper questions on amount of substance and make sure that when doing the questions you use every single value given to you by the question.
Often in backwards titrations they will give the concentration and volume, from that you find the number of moles and plug it into the molar ratio in the equation to find the moles of the desired product or reactant, from there you can multiply it (often by 10) to find how many moles were in the original solution. Then it's nice and easy to find the mass, Mr, concentration or anything else.