Useful
Some people study a certain language because to them, it would be useful in the long run. Others use it for business. What about you? What do you do that makes you need to learn a new language? What kind of people do you usually encounter in your line of business? Would it help improve or even make your life easier? Answering these questions would greatly help you come up with a fewer selection of languages that you could use. Don't even think of studying two languages at the same time. To be able to fully understand and speak fluently a certain language, it would be better if you just focus on just one. Then you can proceed to another one later on. Of course, you can choose not to study another one. But if it is still useful, then you should also consider it.
Want
You need to want it first in order to learn a new language. The willingness to learn a new language is the key to everything. It would make studying and everything else that comes along with it a whole lot easier. Just maintain that eagerness all throughout the studying period. And besides, even if you don't have to learn one, you will also have fun studying. That drive will take you places. And who knows, you might need that tongue sooner or later. So by all means, go for it.
Time/Convenience
You know, you can always waste your free time on watching TV, listening to the radio or surfing the net. Of course, you will do all these and study at the same time. This is because, you can watch TV shows that use the language you want to study. Audiobooks are available, too. Last but not the least, many websites offer online tutorial and lessons. With all the new technologies that we have nowadays, having not enough time is no longer an excuse to not being able to do something or anything. Multi-tasking is definitely the word that best describes what everyone is doing. But if you don't think that you could take all the stress, then don't do it. Just take one baby step at a time. For example, you can study a new word per day and try using it in your daily conversations. On the other hand, if you have all the time in world, going to school that specializes in teaching a certain language is the way to go.
Budget
If you have loads of money to burn, then you can always enroll in a good, if not prestigious, language school. There you can try speaking, comprehending, and engaging in conversations with people who talk with the same tongue to your heart's content. Teachers are also available for consultation. But if you can't do that because of lack of funds, there are always a lot of available cheaper alternatives. Like the ones mentioned above, you can try listening to audiobooks, which are available in some libraries for a rent or for free. This is best if you have chores to do around the house. But if you just sit in your little office cubicle, then spending your break time browsing for sites that offer online tutorials is a good idea. If you get lucky, you might come across one website that offers it for free.