How good of a grammar book do you have? If you just learn the rules of Spanish then it's a lot easier than learning every single example. For example, let's focus on gender. I know you Germans use THREE genders but this is a good example.
You can "notice" that words that end in "umbre" tend to be feminine in Spanish. Alternatively, you can just remember the rule and apply it to every situation. You really only have to remember like 15 gender rules to get the gender of almost every word correct.
La muchedumbre
La cumbre
Indefinite vs Preterite:
Preterite: used for a concrete action.
"FIVE days ago I saw Anchorman 2 at the movie theater." (Hace cinco días vi la película Anchorman 2 en el cine)
Indefinite: An event that can't be described at one specific point in the past. Or just a description of the past.
"When I was young, I liked to go fishing." (Cuando ERA joven me gustaba pescar)
Subjunctive vs indicative.
Subjunctive: used when you have a change in pronoun and emotion, doubt, possiblity, need.
YO necesito que ELLA estudiE español.
YO QUIERO que ELLOS me traigan el pastel.
The subjuntive is also ALWAYS used with certain sentence constructions.
A MENOS QUE sepas cómo hacerlo...
CON TAL DE QUE me ayudes con mi tarea...
PARA QUE lo tengas claro, te voy a explicar cómo...
These "special sentence constructions" have to be memorized, plain and simple.
Finally, there are "Adverbial Clauses" that MAY or may not require the subjunctive.
CUANDO la veas, dile que la quiero.
AUNQUE lo intentes, nunca lo vas a conseguir.
Good luck; let me know if I can help you. (PS, we could talk about German, I've always thought about learning it) :)