There are a lot of textbooks that you can use to start building your Spanish vocabulary, but some of the best things you can use are Spanish newspapers, books, magazines and television shows. These media use the most basic Spanish words used in a conversational context, giving you a more direct approach to the actual usage of the Spanish language. Make sure that you have a handy Spanish dictionary when reading or watching so that you can easily look for words that you are unfamiliar with.
If you are an auditory learner, you can also download or buy Spanish audiobooks that you can put on your digital MP3 player. Listen to the audiobook while driving, running or even when cooking. To start, get some audiobooks that teach Spanish for beginners. These types of audiobooks usually teach the basic Spanish words, as well as basic grammar rules. If you're a bit familiar with the language, you can then try listening to Spanish radio stations with Spanish speaking disc jockeys. This will help you recognize Spanish words more easily and understand how the vocabulary is used in everyday life.
The easiest way to improve your Spanish vocabulary is to speak in Spanish --- especially if you're talking to native speakers. Options include a Spanish-speaking friend or a friend who's also learning the language. Using the language not only helps you to practice, but also supplies you with an arsenal of new words. Like anything in life, the more you practice, the quicker you'll learn.
Don't stuff your head with a long list of terms that you might not even use. Make your Spanish word list more interesting and prioritize what is important --- usually focusing on commonly used words. For example, if you like cooking, make a list of ingredients in Spanish or go buy a Spanish cookbook. Once you are familiar with the words, write your favorite recipes in Spanish. This strategy will sharpen your vocabulary better than just listing Spanish words that are not directly involved in your day-to-day interests.