When considering what will be the most effective strategies for you, don't forget the basic principles of memory:
(1) Repetition repetition repetition
The trick is to find a way of repeating that is interesting to you. This is partly governed by level of difficulty (too easy is boring; too difficult is discouraging). The point is to find an activity (more than one, in fact), which enable you to hold on to your motivation through sufficient repetitions to drive them into your head. Bear in mind, too, the importance of:
(2) Changing context
Simple repetition (cat - el gato; cat - el gato; cat - el gato ...) is not only boring, but also the least effective way of experiencing the needed repetition. Not only do you want to see/hear words presented in a variety of different sentences; you also want to experience them in different ways - listening, reading, speaking, writing.
(4) Seek the link
The basis for the keyword mnemonic, and the reason some words are "easy" and others not. Looking for the similarities between words, and being inventive when necessary, is crucial to easing the learning burden, and reducing the number of repetitions you need to fix the word in your memory. It can be as simple as observing that "gato" is very like "cat", or that "el borrego" means "sheep" because sheep are boring.