I think you have to be in touch with the language everyday or, at least, very frequently. This can be done by using so many different methods, if you think about it. Nowadays we have podcasts, youtube videos, books, the internet, duolingo... It's probably a good idea to spend some time choosing your favourite methods and maybe classify them according to the amount of time you have, what do you want to learn, what do you feel like to learn... Think in some sort of schedule where you can also fill in those "dead" moments with input of the language you want to keep up with (listening to a podcast whilst on the bus, etc).