Hi! I recommend you using some textbook as a base. You can easily find for instance ”Дорога в Россию» on the internet. Or buy ”По-русски — легко», «5 элементов», «Поехали!» etc.
Secondly, don't try to learn all cases in one week. Start from the first case, then go to 6th, 4th, 3d, 2d, and 5th, for example. And learn cases from the functional point.
And start with nouns, then add forms of adjectives. Slowly :)