Unless you did RTK or Kanjidamage before you started reading, creating mnemonics is not going to be that easy because you never learned components of kanji and lack a more in-depth understanding of how kanji are formed. You also haven't practiced creating mnemonics for Japanese before. In this case I would recommend not worrying about mnemonics and trying to memorize readings without them.
For example, in Kanjidamage mnemonics for readings are pegged to their system of naming kanji parts. Without learning the system you can't understand the mnemonics and make similar ones yourself. Of course, you can create your own system, but it also has to be based on some clues, triggers. When you see a kanji, you recall its reading through that.
If you did Kanjidamage or Kanjidamage+, you already know ~2 thousand premade mnemonics for kanji readings, and they're going to help you a lot. For me this was pretty much the case. However, the benefits don't last long. Kanjidamage's mnemonics helped me out at first, but I quickly moved past them as I continued to learn new words. And the more words I learned, the easier it was to learn more words. I eventually forgot all the mnemonics I used to know.
Because the benefits are going to be short-lived, I don't see a strong reason to recommend mnemonics. The better you get at Japanese, the less you are going to need to rely on them. I think that instead of creating a system of mnemonics it's better to spend that time on learning a few thousand Japanese words even if at first it's harder.
If you choose to use mnemonics, don't rely on them for too long. You don't want to be an advanced learner who still thinks of mnemonic stories when trying to read every word. To recall something through a mnemonic you have to take an extra step. First you have to recall the mnemonic and then the thing itself. Reading Japanese should be automatic, like reading in your native language.