This website teaches every vocabulary and grammar topic that you will cover in all of middle school Spanish. Look for the topic you need help with on the left, read the tutorial, then do the free practice quizzes to test your progress. Only the first few practice quizzes are free, but this is enough to make sure you understand.
You can't help but learn Spanish as you interact with native Speakers in this interactive video series called "Mi Vida Loca".
Choose which types of verbs you need to practice (-ar, -er, -ir, etc...), which verbs specifically, and how long you want to practice.