I've been finding simply reading in the target language to work like a charm. It also helps with understanding how words are used.
But I also use anki. https://apps.ankiweb.net/
There's a free app for android and the desktop app is free. If you have an iphone though it's an absurdly priced $24.
I feel like in the beginning it's necessary to just start memorizing frequency lists. The most common words. After that you can start to pick up vocabulary in situ.
Of course, this is just my take. There are a million.
Also there are memory techniques that I have used in the past but don't use very often anymore (not that there's anything wrong with them, I just find them too time consuming). One is a memory palace which hijacks the natural human instinct for having an incredible memory of physical space: https://en.wikipedia.org/wiki/Method_of_loci
Another is to construct a funny image in your head of the word. Arguably this is a lot easier with non-abstract words but it can work with abstract words too if you're creative. For example, to remember poder, you might simply think "Tide pods can kill people." (Arguably this isn't funny, but it should work). You'll (probably) be able to remember the word poder from that, and the meaning is present (can).