Learn a Language

One extremely rewarding experience can be learning a foreign language. Besides the fact that some languages are very beautiful on their own, usually a new language will introduce you to a new culture that will spark your curiosity and stimulate your mind. You can make new friends among those that speak the foreign language, try interesting cuisines, and see beautiful scenery if you travel to other countries. Furthermore, being able to speak a second language looks very good on your resume, because many companies are now making changes in order to cater to a more diverse customer base.

As for which language to learn, these are just a few possibilities:

Spanish is a great language to learn, especially with the increasing Latino population in the United States, because it opens up a new world of people you can converse with. It is relatively easy to learn, both because of the availability of resources and its similarity to English. It is also a very lovely language.

Latin is a "dead language," but regardless of that, I studied it for three years and found it to be very rewarding. Knowing Latin roots has enabled me to correctly guess the meaning of English words I've never seen before. It also helped me to remember vocabulary words when I studied Spanish for a year, because all of the Romance languages come from Latin.

Currently my favorite language is Russian. I really enjoy learning it. It isn't very common in the U.S., but I'm fascinated by it and I think it's a beautiful language. I hope to travel to Russia in a few years, when I save up the money, and for now I'm working on attaining conversational skills. The internet has a vast amount of resources for learning Russian, for which I am very grateful.

Spanish, Chinese, Russian, German, Italian, French, Arabic... the list goes on and on. Pick a language and learn it!

As you read the next section, keep in mind that there are four aspects to language proficiency: literary (understanding what you read), written (being able to construct sentences on paper), auditory (understanding what you hear), and oral (being able to construct sentences aloud). Though written and oral proficiency appear similar, they are separate aspects due to the way the human brain processes language.

A Suggested Method:
First, learn the language's alphabet. Listen to how each letter is spoken, and practice your pronunciation. Gain proficiency with it before moving on to vocabulary. Learn a lot of words, ideally by seeing them in sentences. Repeat the sentences out loud, concentrating on proper pronunciation. If you regularly see and hear words used correctly in sentences, you will slowly gain an intuitive understanding of proper syntax. Learn to conjugate verbs. This can take a while if the language has a lot of different conjugations (Latin is notorious for that).
Once you have a basic set of vocabulary words, try reading children's books. If they are available, listen to children's audio books as well. Gradually increase book difficulty. After you read the books, try to write a summary of them. Over time, stop writing the summaries and instead talk about the books out loud. Find a native of the language and become friends with him or her, and practice your language skills as often as you can. Never worry about looking or sounding silly. Many people are glad to see someone trying to learn their language (including me, for English), and many of those same people are willing to help you learn.

If you are aiming for fluency, your ultimate goal should be to be able to have deep conversations with someone in your chosen foreign language, and to be able to read and write book-quality material.

Online Language Resources:
Word2Word (free)
Mango Languages (free limited trial)
BBC (free)
Language Online (free)