Just as with 傷む and 傷める, you’ve already memorized that these are a pair, which is at least half the battle.
While I still think sheer repetition is by far the most important thing, a few other things occur to me that might help:
In addition to sound cues (“moo”) and associations, you can also use things like character length (傾く has two vs. 傾ける’s three) and sometimes specific visual differences in the characters to help remember which is which.
My favorite mnemonic was: 逃げる・逃す — there’s no が in にげる, it escaped!
They don’t have to make sense, though, they just have to work. I’m embarrassed to even write this because it’s so non-sensical, but with this specific pair I focused on 傾く (the intransitive version: something is tilted or leaning). I noticed the く kinda points inward, toward the kanji before it, so I told myself that this is the INtransitive version, it acts on itself (geez that seems tortured now that I write it down).
Further, as someone mentioned above: memorizing a single Japanese sentence using one of the words often suffices if you know both versions pair.
In this case, I imagined my mother-in-law looking at a crooked photo and saying 「この写真が傾いてる (with a very strong emphasis on the が). It would sound very weird/off/wrong for to me to hear 〜を傾いてる now.
For some bizarre reason, I have very specific characters in my head talking to me all the time as I do my reviews (voices in my head explain much to and about me!).
I honestly hear them in my head! My mother-in-law appears quite often, as does じょうぜんさん who was a senior manager at one of the resellers I used to work with (I suspect it’s 定善さん but I’m unsure). Both have very clear, distinct voices, and for some reason I found them easier to understand than many of my Japanese friends and family. I seem to have subconsciously chosen those two voices as my primary imaginary speakers.
My father-in-law was by far the person I had the hardest time understanding. He had an extremely gruff voice, was very terse, and had a fondness for somewhat dated expressions and bad puns. But he still appears in my head during reviews from time to time for things I can CLEARLY imagine him saying!
I mention all this because I think it’s very important to actually hear spoken Japanese in your mind’s ear. It seems beneficial to imagine real Japanese characters who’s voices you know saying these things. It really does help to make things stick. (The main danger, of course, is imagining incorrect Japanese — it can be hard to unstick.)
In particular, memorizing, and hearing, phrases with を for transitive verbs and が for intransitive helps tremendously. Eventually (with enough repetition), it will just sound weird to use the wrong one.
But all of this only takes an instant! I’m no master by any stretch, but the combination of sheer repetition and imaginary speakers has done wonders for me.