I think this depends on how proficient you are, your weaknesses, how you best learn, and what your ultimate goal is. I say the latter because I know people in high school who took 4+ years of Spanish, made it to AP Spanish, and still could not form coherent sentences in Spanish at that point. How that works I have no idea. Anyway, assuming you have a good grasp of the language:
Do you only care to be able to understand the language? And if so, only in written format, for example? In that case you can dedicate much of your studying to reading. What is your lifestyle like? Are you lagging in a certain area, or does your lifestyle demand that you study in a certain way? The latter sounds weird, but I have a personal example. I don’t own a car and therefore spend a lot of time walking or on public transportation. Because I was and continue to be sufficiently proficient in my first foreign language, I take advantage of this time to listen via tons of podcasts. Unless we’re talking a dying language, podcasts should be easy to find on many topics. Maybe start off with news podcasts if you’ve no idea where to start. I have found enough shows that satisfy my interests in history, science, technology, culture, etc. Even talk shows or radio show conversations are great. You can more easily pick up speech intricacies in informal talks that natives use in everyday life. This is a good strategy because even if only one word or phrase marinates in your head after listening, these will add up over time. Importantly, my speech has benefited immensely from all the listening I do. I also think that listening to a difficult podcast, where you might only grasp half of what’s being said, can be helpful. Hearing a native speaker talk that quickly and using vocabulary out of your league will make those things more normal for you, and in that case don’t beat yourself up if it’s simply background noise.
Now, let’s say you want to speak this language and be understood by natives. Certainly the primary goal for most people. Assuming you don’t have anyone in real life with whom you can consistently converse, and you can’t reasonably travel somewhere to immerse yourself in the language (thanks, COVID), then you need to find a language exchange buddy. I’ve used Tandem with some success. I speak with someone for a couple hours at least on a monthly basis, if not more frequently. There are definitely other websites and apps out there for this purpose. If English is your native tongue, then you shouldn’t have much difficulty here because it’s so high in demand. I think it’s better to find a few people who will commit to practicing with you over the long-term. Otherwise you shuffle through different people and discuss the same small talk each time, never reaching more complex topics due to awkwardness/lack of time/fear of offending the other person.
If your skills are lacking despite all the years of study, you might need to find an online course to help get yourself to these levels. I only started learning a second foreign language this year, and it’s in my free time. My vocabulary is low, so it’s difficult to use the methods I previously described. I have to physically sit down and spend X amount of time doing a lesson (I paid for an online course), practicing constructing different sentences in a notebook, etc. Simply practicing constructions (replacing one or two words in an example sentence over and over) in your head or even out loud when you’re doing various activities can help.
Finally, reading stories and watching films or shows in that language will help as well. Things I should do more, honestly. But I did a lot of reading and writing in college, and speech and vocabulary are my weaknesses. So, I prioritize the latter.
I hope that helps. Mind you, to my dismay I have not yet been to a foreign country to practice my language skills, so my perspective could be limited. Language learning also came easily to me ever since I started, and I realize that for others, it is frustrating and or unpleasant. But natives have told me that I speak quite well, so I think my advice has some value. Whatever methods you choose, try to do 30-60 minutes nearly every day. Much like lifting, rest is important, but you also can’t put forth 10 hours of effort one day and then do literally nothing for a month and expect good things.
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