Everybody likely differs (widely!) with their established or preferred methodology for viewing negs/transparencies.
As a beginner almost five decades ago, I used a whale-oil lamp in my parents' beach shack to view, wide eyed and in wonder, my first efforts with early Ektachrome and Kodachrome slides!
I occasionally view transparencies on a simple "lightbox" app on my phone or tablet when I'm away from the man cave. In a plane at 13,000m commuting, holding up slides by the window to the big blue sky outside works a treat too — but getting a snap of them against those irksome windows is not so straightforward.
Otherwise, locked away and in darkness — cutting out all reflected and ambient light is something I enforce when viewing opaque-masked transparencies on a neutral, colour-corrected OLED lightbox. I used a simple and cheap A3 tracing lightbox for a few years before upgrading.
One useful trick to holding negs/strip transparencies down on the lightbox (when removed from the carrier sleeve) is the use a sheet of clear, antireflection OHP presentation media: place the strip of negs/trans beneath and tape down the sheet. The slight warmth of the lightbox will assist in flattening any pronounced curl.
