I am finding it hard to remember my vocabulary words for a longer period of time and wanted to know if there are any tips on retention in relations to German.
Use the language you want to learn!
There is no better way to remember what you have learned than using it.
You've learned how to ride a bicycle and wonder how to do it better? Reading a book about riding bikes will not help. Riding a bike will.
Have you heard of the man who became a well known pianist just by reading books about playing the piano? No? Well, nobody heard of him, because he doesn't exist. You can't become a good pianist without playing the piano again and again. Good pianists play the piano 10 hours a day. Every day. For decades.
And the very same is true for languages: Reading books about German grammar will turn you into a person who can make a good presentation about German grammar and learning vocabulary by heart will fill your brain with lots of new facts. But the effect on the ability to speak the new language is weak.
Speak German if you want to learn German! Write essays in German! When you are here on German.stackexchange: Do not ask your questions in English. Try to write your questions in German. If you make a mistake somebody will edit you post and correct your errors. Find a friend who speaks German and speak German with him or her. Spend your next holidays in Germany or Austria. If you come with your family, speak German with them. (I sometimes travel to London with my wife, and when we are there we do not speak German with each other. We speak English.) Watch movies in German language, read German newspapers and magazines.
If you're not so good at German, start with passively using the language, i.e. listening and reading. But begin as soon as possible also to use this language actively: write and speak German.
And don't worry about memorizing long lists of vocabulary. Nobody who speaks a language does this in real life. You just use the vocabulary that you have. And when the word you need to formulate the next idea won't pop up in your mind, use other words. Build new sentences. Describe what you want to say. This is how everybody else does too.
And do not worry about failing. Those who are good now (in whatever discipline you can think of) failed more often in the past than the average people ever tried.
Another suggestion: stop seeing them as "advanced" German words. There are no "simple" or "advanced" words in any language. Words represent ideas (or objects). It is your own attitude to these ideas or objects that makes you perceive them as "simple" or "advanced".
Become a computer. Humans forget words if they don't use them. We tend to remember words if we live them, though, so human contact enhances your memory.