I have just recently started trying to learn Spanish. Here is what I do, and it seems to work well so far
A) if you can, find a beginning Spanish class at a community college, one for adults, or something similar. This will teach you the basics and motivate you to learn
B) Post on this message board or other sites, but respond in Spanish as much as possible. Having meaningful conversation with people in another language will motivate you to get better.
C) I use the following for an online English-Spanish dictionary: www.wordreference.com. If you speak one of the main European languages, this site will help you learn a lot about the Spanish language. You can use it to look up common expressions or conjugations of any verb.
D) I use the following for translating sentences I don't understand: http://babelfish.altavista.com/. Another great use is to type in sentences in your native language and see how they would translate. Of course, the translator cannot always provide a perfect translation, but it is better than nothing.
E) Find a website, perhaps your favorite website, and see if there is a Spanish language version of it. Find an article on the site and try to read/translate it. If you have any doubts or confusion, come to this site and ask about it.
F) Practice often. Try to read and write something in Spanish every day. You have to be committed to learning.
G) It is very important to learn the rules of grammar. For instance, you should understand what verb conjugation is, the difference between preterite and imperfect tenses, etc.
That is my advice to you.