It depends on what you need to learn. For me, flashcards work really, really well for memorizing vocabulary. Make a flashcard for each vocab word with the English word on one side and the Spanish word on the other side, and keep quizzing yourself until you can get through all the flashcards on the first try.
For learning things like conjugation, practice is probably the best way to learn. You can try the website www.conjuguemos.com. I don't know if you need to pay to have an account with this, but my high school teacher had it set up so that each of us students had our own account. You could pick which tense you wanted to practice (imperfect, present, subjunctive, future, etc.), and then it would give you a verb and a pronoun, and you would try to conjugate it correctly. You get immediate feedback, and it's an excellent way to practice.
Finally, depending on how much time you have, it might also be helpful to put the Spanish subtitles or spoken language on a movie you like. For me, it helps me to get a good feel of general sentence structures, plus you can pick up new vocab.
Good luck!