Here's a question I've gotten a lot recently, in some form or another: How clear should my visualizations be?
Here's my experience, and this goes for both learning applications and memory sports: A key thing to realize is that the visuals themselves aren't always that important, so I don't worry if my images aren't clear. They’re often just fuzzy impressions. The memorability often comes from the story or narrative, simply the idea that image A is interacting with image B (or a particular location) in a semantically interesting way. I blogged about this following my 2015 USAMC experience, and for those interested in digging a bit deeper, that post explains the idea more clearly. When it comes to long-term recall, this idea becomes even plainer. If I haven't recalled something in weeks (or especially months), my image has usually been reduced to its most basic form: an idea in a location. For example, when recalling that toxoplasmosis is one of the clinical uses of the drug combo TMP-SMX, I just have a notion that there is a cat (toxo) on my elementary school's stage (a locus in my TMP-SMX area). No salient sensory impressions, generally--although of course some unique visuals or tactile impressions may stick here or there. I just know there's a cat on that stage, and that's all I need.
Update: More recently, I wrote about the benefits of using palaces--rather than just standalone images--and #3 of that article touches on the "idea in a location" point discussed above.
Headspace, a meditation app I use, has a great video about making visualization effortless. I think the same principle applies to memory visualizations.