Repeat it, write it, check the meaning with a native speaker/dictionary, and read some example sentences. Go and have a cup of coffee. Come back and see if you can still remember it. See if you can use it in a sentence (and get it right, of course!). You'll need to check with someone to make sure it is USED correctly! Write it down in your diary somewhere in the future. So if today is the 3rd, put it on the page for the 20th. Now do some other work, have a night's sleep, go on holiday, forget about it. And then on the 20th you'll open your diary and there is that word. Ah! What did it mean? Can you write it in a sentence? Have you got it right? Well, I think that if on the 20th you can remember, and use that word, then it's in your brain pretty firmly! Actually there are some sophisticated apps to remind you about vocab revision, but a piece of paper and a cup of coffee is really all you need. And then YOU MUST SPEAK and USE the language. MUST MUST MUST! SPEAK SPEAK SPEAK.

I think it is safe to say flashcards are the best way to memorize and retain any kind of 1:1 information like vocabulary. You can make your own with paper and pen, like we did before computers were invented ;-) I highly recommend the Anki program for studying vocabulary. It is similar to the Brainscape apps on iOS, but Anki is free for PC, Android, and MacOS. Anki's iOS app costs US$20, which is a little outrageous. Both of these apps let you choose how well you remembered the word, and then show the words you've learned less frequently while introducing new words.

Flash cards work for me. As always you had to continue to hear them. You can't memorize a word and then not use it . Of course you'll forget! You have to keep on saying it and using it

I want to increase my vocabulary. I am trying remember more and more words, but soon I forgetting half.

Can you describe what properly remembering a word means to you?