Spread the same study time across several days
With the same total study time, several sessions generally produce more lasting recall than one session. A synthesis of 317 experiments examined this effect. A useful broad principle is that the longer you need to retain something, the longer the interval between reviews should be. Reviewing today may suit a test tomorrow; a test a month away allows reviews several days apart.
What it takes
No money or extra total time. Divide, for example, three hours into one hour on each of three days. This requires starting early enough instead of waiting until the last night.
What you may gain
A meta-analysis covered 184 articles, 317 experiments, and 839 assessments of distributed practice. It examined both spaced versus massed study and shorter versus longer spacing. The interval between sessions and the desired retention period jointly determined final recall: longer retention goals were associated with longer optimal spacing. A separate review of ten common learning techniques rated distributed practice as high utility.
Context & considerations
Combine this with self-testing by spreading the tests themselves across days. Much of Cepeda's evidence involved materials such as word lists; it does not provide one universal optimal interval for complex subjects. “Longer retention, longer spacing” is a general pattern, not a fixed schedule. Cramming can help immediate performance, but the learning fades quickly.
Research & references
Cepeda NJ, Pashler H, Vul E, Wixted JT, Rohrer D (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological Bulletin, 132(3), 354–380. https://doi.org/10.1037/0033-2909.132.3.354; Dunlosky J, Rawson KA, Marsh EJ, Nathan MJ, Willingham DT (2013). Improving Students' Learning With Effective Learning Techniques. Psychological Science in the Public Interest, 14(1), 4–58. https://doi.org/10.1177/1529100612453266