Now for the answer.

There is no easy way. Everybody learns things different ways, and you need to find your own. People can give you ideas to try, and there are a couple of good ones here. I have similar problem – learning grammar rules comes easily to me, but the general vocab comes much harder. One way of improving your vocab is similar to the flash cards idea above, but for simple nouns (ie real objects e.g. ‘table’, ‘chair’, ‘window’, as opposed to abstract nouns which refer to something you cannot touch, like ‘art’, ’science’, and ‘chaos’) you can stick the card to the item, and every time you see the object, you see the word.
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Apart from that, one of the best memorizing aids you can use is flash cards. Make hundreds of small pieces of paper of the same size, on each you write a word from the language you’re learning on one side and the corresponding English (or whichever language is your mother tongue) on the other. Then you can make sure you not only know the words from a list in the same order, but also when they come in random order. Always carry a bunch of these cards in your pocket – you can check some words everytime you stand in a queue, in an elevator, at the toilet, just before you fall asleep in a tent, and so on, without having to carry any books. Highly recommended!

For some languages (like Chinese and Japanese) you can by printed flash cards, which can be of great help for a beginner, especially if you have troubles writing their characters properly, but normally the actual writing and preparing of the cards is in itself a useful part of the study.

Also, I would really recommend you to be very careful about the correct pronounciation of the words (and writing, if it is in a foreign alphabeth, like Russian or Greek) already from the beginning, so you don’t have to learn them two times (learn and then relearn them differently). Some people think it’s ok if you have an approximate pronounciation, and then you can fix it better later, but all my experience tell me it’s worth a lot to have it properly from the beginning. Very often, people tend to confuse the later correct pronounciation with the approximate pronounciation they learned as beginners (that still lingers somewhere in the "automatic" part of your brain), which means they will never reach a good overall pronounciation of the language.
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Own experience from learning many different languages through different methods.

memorize.
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