Humans forget newly learned material in a matter of days (red curve) unless reviewed from time to time (green curve). Don't think you can memorize items in a single learning session. Repetition is key to retaining memory. See Forgetting Curve for more.
Items memorized, however extensively, in a short period of time will not last long. Leave some time in between reviews, and spread out the repetition into a longer period. Furthermore, gradually increasing the repetition interval will allow you to keep things memorized very efficiently.
Instead of reviewing passively by reading notes or selecting the correct answer to multiple choice questions, actively recall what you've memorized by answering questions. Use flashcards with questions on the front and answers on the back to help you do this.
There's an infinite amount of information out there and you can't memorize them all. Memorize only what you need to memorize by creating your own set of flashcards.
Instead of attempting to just rote memorize, first understand what you are about to memorize. For example, you should understand that the Japanese word "ankimono" is formed from "anki", which means "to memorize", and "mono", which means "thing", before memorizing the word, which means "things you just need to memorize". Understanding before memorizing will not only allow you to memorize more easily but will also let you apply your basic understanding in other situations.
Especially when memorizing things that don't accompany understanding such as sequences of numbers, use mnemonics where applicable. A good example is knuckle mnemonic for remembering the number of days in a month.