An oversized T-shirt is supposed to look relaxed, but there is a difference between intentionally oversized and simply looking swallowed by fabric. The easiest way to make the shape work is to balance volume: if the tee is loose, give the rest of the outfit a little structure, definition or contrast.
Embroidery helps because a small stitched motif gives the eye a focal point without turning the T-shirt into a giant graphic.
Start with the proportion, not the trend
The most useful styling rule is simple: decide where you want the outfit to have shape. Straight or wide-leg jeans can work with an oversized tee when the waist is visible through a small front tuck. Leggings work because they create contrast against the looser top. Tailored trousers work because the clean line of the trouser makes the T-shirt feel deliberate rather than sloppy.
With denim: the easiest version
Denim is the obvious partner because it gives an oversized cotton T-shirt some structure. Straight-leg jeans are the easiest option; wide-leg denim works well with a front tuck; shorts keep the silhouette light in warmer weather.
With tailored trousers: make it look intentional
A loose embroidered tee with tailored trousers is one of the easiest ways to make casual clothing feel considered. The contrast between a relaxed top and a clean trouser works particularly well when the embroidery is small.
With skirts: keep one clean line
For skirts, think about where the T-shirt finishes. A full tuck gives the clearest waist. A loose tee over a straight midi skirt creates a more relaxed column. If both pieces have a lot of volume, a small tuck at the front or side usually stops the outfit feeling too heavy.
Layer it without hiding the embroidery
The chest detail is part of the point, so layers that stay open work best: an unbuttoned shirt, lightweight jacket, blazer or cardigan.
Choose the size based on the silhouette you want
An oversized fit already includes extra ease, so sizing up again changes the silhouette quite quickly. Stay close to your usual size for a relaxed oversized look; move up when you deliberately want more length and volume.
The short version
Keep one part of the outfit defined, use texture and tailoring for contrast, and let the small embroidery act as the detail. Oversized does not need to mean complicated.