If an A-level is a B1 and you have reached that level in all the languages (French, Spanish and Russian) you mentioned in the tags under your question, then you can combine studying grammar (there are a lot of good resources which can guide your learning according to your actual level of knowledge) with language immersion.
Reading. Even if it may sound like an obvious suggestion, reading whatever material you have at your disposal (and that is written in your target languages) is the best way to improve your reading abilities and your vocabulary at the same time. In the view of the fact that you have already reached a B1 level, you can try with some blogs and books with an easy plot (for example, if you like comics and graphic novels, you can start with them as they have some illustrations that can help you to have a better understanding of what is going on). Also, when you read a paragraph, try to highlight the words and expressions you can’t understand at all and underline the ones whose meaning you can only guess. Then, search for their meaning, write it down and reread the paragraph to understand it better this time.
Listening. Like in the case of reading, the best approach you can adopt considering your actual level is to practice your listening by listening to people talking in your target languages. If you can’t do so in real life, you can at least watch whatever program, tv series, movies, documentaries or Youtube videos you want and listen to podcasts. Also, audiobooks can be a good way to improve your listening as they make you stay focused on listening if you want to understand what is going on.
Grammar: some new rules plus review of the old ones. On the Academia Pradoventura website there is a Spanish Grammar B2 section while on the AmautaSpanish there are many exercises for Spanish grammar for all levels. As for French, you should try the Étudier en France: French Intermediate course B1-B2 on Coursera. Also, again on Coursera you can find the Русский как иностранный: B1+. Russian as a foreign language: B1+, which is offered by the Saint Petersburg State University. Finally, if you want to revise some grammar you should already know while using books written in your target languages this time, on the Books4Languages website you can access for free the Gramática del Español Nivel B1 textbook plus books for Russian and French grammar up to A2 level fully written in Russian and French, respectively.
Finally, organize your weekly schedule in a way that lets you spend time on both improving your grammar and immerse in your target languages (for example, you can spend 30 minutes on grammar and an hour or more on language immersion). Also, try with different combinations of time management (for example, one day you can focus more on Russian, the next one on French and the other one on Spanish while you can still spend a little time on each language every – or almost every – day).