I have test weeks, which basically means that you get about 10 tests crammed up in 4 or 5 days. You need to study a lot for them

so what I did last time:
(10 days before first test)
- turn mobile phone off (stayed off for 2.5 week)
- write down all that needs to be done per subject with time needed, and make an order in relevance of tests and subject material. Focus on the most important things, and if time is left focus on the other stuff too.
- make summaries, definition lists and repetition/flashcard lists (wrts.nl) and organise all material (including practise tests and answers) in google drive maps
(7 days before first test)
- I have class for each subject once or twice a week, so I studied each subject the day before I had the class for a subject as if I had the test the next day
(days leading up to corresponding test)
- study all material again
- practise
- if time left, cram the material (tests here are based on insight, so knowing the exact definition or the six causes of something or the names and dates something happened or whatever is not as important)
Last time it was very successful with an 8.5 out of 10 average which is very good in the Dutch education system.
As for the studying itself, it really depends on the subject. For maths and chemistry all I do is practise. For biology, philosophy and geography I read through the textbook a few times while focused and try to study the concepts and think of examples and read articles about it. For ancient Greek I look up research on texts and study the whole texts out of my head, including the references/pronouns, grammar, stylistic devices, translation, meaning, etc.