An obvious one is just to use them a lot! The more you use a word when you are speaking, the easier it is to remember it.
Another method is something like 'flash cards' in the old days, these were physical cards, with the word on one side, and either a picture, or the meaning in another language on the other side.
Nowadays, you can get programs or apps that do that for you. They are a bit cleverer, as they remember what you got correct. I use one called mnemosyne, and there is another one called anki.