The plot goes along these lines: Years of German classes at school, painful hours spent learning declinations tables by heart, lot of frustration, and after all this pain not even being able to have a conversation with a German person.
It is a common plot, and I think the way to avoid the sad end it is very simple: do you want to learn German? Forget about learning the declinations!
In this post, I argue that if you want to learn a complex skill, in this case, German, you should start by focusing first on the most basic and essential aspects of the skill, and only once you have mastered the basics you can refine your skill.
Learning a complex skill like German by focusing from the very beginning on things such as declinations is the equivalent of starting to think about the furniture for your house when you are still laying its foundations.
By focusing on the wrong things you risk to waste a lot of time that you can use to learn well the basics of your target language. Even worst, starting from the most complicate and difficult aspects of your target language will paralyse you and lower your learning-momentum (that kind of enthusiasm when we think that we can learn and do anything) which is very important to drive learning.
Some people argue that when you are learning something new you should learn everything perfectly from the very beginning in order to avoid creating bad habits that are difficult to eliminate later. While I find this theoretically interesting at a practical level I find that this has the effect of paralyzing the learning process or at least to slow it down.
At the contrary, starting from the basics will create momentum. The most difficult part in the process of learning something new is not keeping going but it is winning the initial attrition and start moving.
When comes to German this translates to very simple advice: ignore complex rules and focus on learning the most basic things this will allow you to start communicating and understanding (initiate movement), then add gradually incrementally difficult things to learn (keep moving), but only when the simple stuff is already taken care of and it feels sort of automatic. This means that you should start thinking about declinations only when you can already speaking and understanding with no effort. Starting from the most basic aspects of German and just ignoring declinations has helped me a lot. It allowed me to start speaking without worrying too much about getting everything right from the beginning and, by doing so, it gave me more chances to practice the language.