Don’t forget the power of sheer repetition.
People tend to underestimate the number of repetitions required for some items to truly stick.
To give you something quantitative (this is nothing to brag about) I’ve burned a little over 5000 items here in about 2.5 years of once-daily reviews. Roughly 2000 were burned in 8 reviews (it surprises me there were even that many, but I had a moderately large verbal vocabulary before I started). Another 1000 or so needed between one and two dozen reviews. The remaining thousand needed several dozen reviews. Two required over 100! And this didn’t count out-of-band study.
As @yamitenshi points out, vocabulary is what matters in the end, and vocabulary reviews help tremendously to make individual characters “stick” — because they effectively give you more reviews as well as additional context.
I’d strongly encourage extra-study sessions of recent lessons (or the excellent self study quiz user script) before any script that mechanically unlocks vocabulary items.
In my opinion, there are two modes: guruing recent lessons (short-term memorization) and recall of older items (long-term memorization). I feel strongly that both fall to sufficient repetition, but how you accomplish that differs.
For short-term memorization, it’s important to have several reviews of new items per day or even per session. If you answer a stage 1 or 2 item correctly, it’s rescheduled for 4 or 8 hours hence. Since I only perform one session per day, that always meant I wouldn’t see it again until the next day’s session. Making sure you have at least two or more sessions throughout the day, every day can help with recent-lesson items, but my recommendation is out-of-band reviews with extra study (or self study).
For long-term memorization, I think the biggest problem is items that don’t fall back far enough! Items that keep falling from enlightened down to guru-2 then back up to enlightened, then back down again are particularly problematic as the reviews are spaced weeks or months apart when you really need more frequent reviews.
When I notice an item that I’ve seen (and missed) too many times like this, I’ll sometimes intentionally answer incorrectly a few times in a row (even after I know the correct answer) just to ensure it falls back farther and is scheduled again sooner. In other words, if I feel I’ll benefit from more frequent reviews of an item, then answering correctly is precisely the wrong thing to do!
Using extra study for recent mistakes can also help with long-term memorization. No matter what: more frequent reviews will never hurt.