Sign up for a Spanish class at the local community college, university or Spanish cultural center. Attend all classes and do your homework.
Begin with the greetings and common phrases. Learn the words for "please" and "thank you" and phrases such as "speak slower please." Expand your vocabulary to include nouns as you move on to objects and days of the week.
Get a good Spanish grammar book. Go to the library and see what it has. Ask the librarian for a recommendation if you aren't sure what to look for. Then go and buy a personal copy so you can write notes in it.
Start a Spanish vocabulary book. You can list the words alphabetically, by the day you learn them or by the parts of speech -- nouns, verbs, adjectives -- to help you keep track of the new words you learn. Review your vocabulary words regularly.
Memorize the irregular verbs, particularly "ser" and "estar" as they can be used in combination with other verbs. Learn the "ar," "er" and "ir" verb endings. Spanish has 17 verb tenses, but you can get away with three, the "presente," "preterito" and "futuro."
Subscribe to a Spanish newspaper. As you read the articles on the front page, underline the words that are similar in Spanish and English. You may be surprised to find that you already have quite a good Spanish vocabulary.
Listen to Spanish radio. Learn to hear the rhythm of the Spanish language and repeat as many of the announcer's words as you can to increase your vocabulary.
Write in your Spanish diary every day. Download a translation program and record what you did during the day. Your vocabulary will improve with writing, because you will begin to see the patterns of the way words are used in Spanish.