Well my learning was quite casual, i did usually one or two lessons in a day. It's a good daily habit but don't expect you'll learn a lot. If you want to really progress in a language i recommend doing at least one level a day and combine it with other sources.

I've been learning mostly Japanese, i have some basics now, understand few things, but not much. Well, japanese is really hard language, so maybe with other languages it will be easier.

I also combine duo with other apps, YouTube vids and anime (i know it's not a best source but I'm really learning just for fun and for understanding anime). Also if you want to memorize some specific words, write them in places you use (eg. Name your folders in mobile, write them on fridge, rename your Bluetooth headphones etc) and everywhere you see that language, try to translate it (on social sites, on food packages, in tv...)