Successfully learning Spanish is about practicing the language, contextually and aloud, in a natural conversational setting. By immersing yourself in opportunities to speak with other native speakers while allowing for only minimal 'outs' to revert back to English, understanding the new language will occur quickly and efficiently. Though not necessarily easy. All other learning—memorizing vocab, verb conjugations, reading, writing, etc.—is important, but fundamentally pointless unless you're also learning to speak. It's taken me years to realize this.
That said, as long as you're getting in daily conversation practice, Dorothy Richmond's Practice Makes Perfect: Spanish Verb Tenses is an excellent learning supplement for the Spanish student. The worksheets range from simple fill-in-the-blanks to more substantial paragraph translations, with each chapter starting with a succinct explanation of a particular verb conjugation.