Visual mnemonics are solid for N5/N4 but you hit a wall around 1000 kanji. The Heisig approach works if you commit to it fully - half-assing it is worse than just doing Anki.
What actually helped me: writing practice. Physical pen on paper. Your brain encodes the motor memory differently than visual alone. Try copying sentences from your reading material rather than isolated characters.
Also - are you testing recognition or production? For JLPT you only need recognition up to N3. Don't burn energy on production if that's not your goal.