The best solution to solve the problem is using that vocabulary. Other nice way is establishing such as a relationship between the word you want to aprehend and one another from your native vocabulary. In order to "learn" the declensions the best way, I think, is know what they want to mean (after memorizing them). For example, in order to make more easier this sort of learning, try to find a relationship between a case (ex.gr., ablative) and daily-use expressions, such as: "de iure" (aproximately, I translate it to English, "by the rule of Law" or "by means of the Law"), you know "de" -in this case- must be followed by an ablative... iure, is ablative. One another: You want to memorize the word "ius/iuris",
Ignorantia iuris (genitive) neminem excusat.
(The ignorance of the laws never exempts from observe them)
This ways may be useful to you when you are aprehending new vocabulary... but I -personally- prefer construct sentences, practise with compositions, etc., because by means of this I am -really- aware of I have learnt the new words and their use.
Verus enim amor semper tempore tristi elucescit magis. (Philipp Melanchthon: Decl. de studiis Linguæ Græcæ)
Quin age, si quid habes (P. Vergilii Maronis Ecloga III:52)