Shoot for the thumbnail, not the detail page
Before anything else, look at your photos at the size they will appear in the grid. Shrink one on your own phone. If you cannot tell what it is in half a second, nothing else about the picture matters.
That one test changes how you frame: closer, simpler, fewer props.
Daylight, near a window, not in the sun
Direct sun makes hard shadows and blown highlights. An overcast day or a spot a metre back from a window gives even light that keeps colour true, which matters because a returned item usually starts as a colour that was not real.
One background, used every time
A sheet of paper, a wooden board, a painted wall. The consistency is the point: a grid where every photo shares a background reads as a shop, and a grid of mixed backgrounds reads as a folder of pictures.
Show scale when it is ambiguous
A ring, a candle, a bag: the buyer cannot tell the size. One photo with a hand, a coin or a familiar object answers the question that otherwise arrives as a message, or as a return.
Keep the files sensible
A square crop, a few hundred kilobytes each. Enormous files make the grid slow on a phone with two bars of signal, and slow is indistinguishable from broken.
Load them once
Products can be loaded from a CSV file saved from a spreadsheet, so you can prepare names, prices and photo links in one pass rather than one product at a time. The storefront is described on Telegram Mini App store, and plan limits are on Pricing.