Decide what type of Spanish you want to learn. Not all Spanish is the same -- it differs a bit from country to country, and in a few significant ways between its form and content in Spain and in South America. Determine which approach will be most useful for you. Keep in mind, however, that even though Spanish varies from location to location, you'll generally be able to understand most Spanish speakers throughout the world.
Gather materials and compile a syllabus. If you are not going to take formal Spanish classes at a college, language school or community center, then you will need to follow their plan and use their resources. Online programs have their own suggested guidelines as well.
Find a study or practice group. Learning a living language requires regular practice, which is much easier and more effective when carried out with others -- especially if they are native speakers. Some websites often feature meeting announcements by individuals or groups for practicing Spanish. Of course, make sure the group is legitimate and plan to meet in a public place.
Practice, practice, practice. For many learners, new languages come slowly. Regular practice speaking, reading and writing Spanish will help you adapt to thinking in and comprehending a new language. Mix your learning methods and have a group with which to study.