Hello people.

In the past I learned the jlpt vocabulary of level 5, 4, and a part of level 3 by using hiragana and katakana. after that I started with RTK. I know about 425 kanji now. I still remember all the words I learned and I now want to learn how to read and write them with the kanji. So I've made a new deck with anki with all the words that have kanji that I currently know of jlpt5.
most of them are obviously very simple. But I was wondering how you go about learning words that use more than 1 kanji and are not self-explaining at first sight.
example: 大切 which means "important"
Do I have to make some sort of story for myself like I did learning the individual kanji that relates "big" and "cut" to "important". is this the way you do it?
My plan is to learn to write and read words like this until I reach jlpt3. from there I want to do the same thing with the difference that I will learn the words used in a full sentence instead of them being isolated. What do you think? any advice? right now I'm only using jlpt lists to get to know the language. I'm not interested in taking a test (yet). Also If you have a source where I can find some practice sentences for these words I would like to have it. (my other sources are minna no nihongo and internet).

Most people just brute force it with flash cards instead of trying to do vocabulary mnemonics. For the most part, they aren't too difficult, because you will typically not have more than 2 or 3 kanji per word, if that. Also, you will see the same readings get used over and over in different words, so if you learn multiple words with the same kanji, they reinforce each other.
Because the number of words in a language is practically unlimited, mnemonics aren't really the best way to go I think. But they could be useful in situations where you just have a lot of difficulty with a particular word.

I think there is no problem with learning words in isolation as long as they are simple words. When you get to more difficult words that are kinda strange in their usage, its a lot more important to have some additional context around them though.

Not much point to mnemonics. There are way too many words to learn.

I've been experimenting with all kinds of methods, and in my opinion the best way to go about building vocab is to first drill sentences, written in Kanji, but with audio in the question. These should be relatively easy to do, even if you're not confident in your Kanji knowledge.

And then, in a second stage, drill either the words in those sentences, or the same sentences, without audio in the question. If you haven't done RtK, I would suggest sticking with sentences in the second stage as well, at least for a while (because doing individual words would be too confusing without being able to easily recognize the individual Kanji - too many words would end up looking alike). Or at least add the sentence the word comes from, to the question, to help you out when you're stuck. Over time, this second stage can be replaced by just reading level appropriate native materials instead.

And of course immersion is the most important thing. No point in drilling anything if you don't use tons of immersion to help you understand the actual language in its natural state.

I don't use mnemonics normally, but for every word I do have a context sentence. Many simply come from checking the dictionary at dic.yahoo.co.jp, if my word doesn't have a good sentence there I check alc.co.jp and tatoeba.org. There used to be a couple others I checked but I don't have them in my bookmarks on this computer. (You want to be careful not to choose sites that overlap the same database; most dictionaries and sentence sets have multiple services that use them.)

Anyway, if I'm still failing a card for too long, I'll come up with a mnemonic to make it stick after trying simple memorization first. 大寒 for example, I would be randomly guessing at whether it was たいかん or だいかん every time the interval got to be a week or so, and I'd fail it again sooner or later, so I finally thought about how it sounds like 大根, and maybe you need to have all your 大根 harvested before the 大寒. Yeah it's dumb, and I don't even know when daikon are harvested in reality, but it made it stick. Most of my mnemonics are like this - for a specific consonant voicing or devoicing question, or a specific long vs. short vowel problem. Most words stick without a mnemonic and the ones that don't, I usually have them 'roughly' right and just need the mnemonic to get them perfect for a few weeks until they settle into long term memory. Don't worry about how dumb or terrible a mnemonic is - just give it a shot. If you forget the mnemonic you can come up with another one next time. But don't invest time in mnemonics anything like you did for RTK - use them only when you have to, and don't think about them too hard.