Do not bother learning them until B2 level. Case endings are redundant is most cases assuming that your sentences are grammatically correct. Use singular/plural noun in nominative form if you do not remember correct form. It is much easier for native speakers to deduce the right case than mentally fix serious spelling mistake.

I am sure that learning endings is important but useless without regular PRACTICE. Don't focus on learning ALL endings by heart. Try to remember some of them and put them into practice. Move forward step by step, practice what you have alredy learned and you will see that you master these scary cases))) There is experience of the girl who has been struggling with Russian cases for a while: http://www.fluentin3months.com/russian-cases/ She describes her own techniques. Hope they will be helpful for you. Good luck!