Before I decided to finally take language classes, I used to self-study on my own. And for a month, I managed to get an entire lesson in. Like you said, having a good reason to learn a language is a HUGE motivator. It could be for someone you like, a future career opportunity, or, in my case, simply being able to watch a damn show without English subs. I used to set aside at least an hour a day to learn a topic, so I highly recommend a schedule as well.
I never tried these myself, but also give yourself an incentive to learn a language, too. Treat yourself if you can memorize "x" amount of words in a week or if you are finally able to grasp that one concept you've been struggling with. Or have study dates if you know anyone else who is trying to learn the language as well. When you actually have to plan to meet up to do something (which entails showering and getting dressed...), I think that'll give you the extra push you need, even if you a lazy ass like me haha.