A foundation shade might look perfect on the back of the hand yet look incorrect on the face. Your hand has different depth, undertone, and redness levels than your jawline, neck, or central face. For that reason, many first makeup applications start with a base that looks acceptable inside but looks too orange, too pink, too light, or too flat by the time the entire face is complete.
A better place to swatch foundation is along the jawline, at the boundary between face and neck. Apply two or three slim strips of candidate shades running from the low cheek down the jaw. Do not fully blend them at first. Allow each strip to sit for a second, and notice how each blends both into face and into neck. Ideally the best matching shade will not show as a separate stripe against the skin. It should be unobtrusive, even before you apply concealer, powder, blush, or bronzer.
Undertone is as important as depth. A shade can be the right lightness or the right darkness yet look slightly off due to an incorrect undertone. Some foundations are warmer and display as yellow, peach, or golden. Others are cooler and display as pink or rose. Neutrals are somewhere in between. An orange tone at the jaw might be too warm or too dark. A gray or ashy tone might be too cool or too light, or not appropriate for your complexion.
Start with less product while testing. A heavy swatch may mask the true finish, as too much product can give you the impression of better coverage. Start with a very thin layer, and add just a little more where you feel you need more coverage. This also helps you determine whether the product gets muddy, digs into skin texture, or starts to appear cakey. It is easier to gauge the base you like when you use as much product as you would wear in actual use.
Lighting can affect your judgment. Bathroom bulbs, incandescent bulbs, and computer or phone screens all give you the wrong impression regarding whether a foundation shade looks good. Test the shade along your jaw, and if you can, check that shade near a window or under some daylight. You do not need perfect studio lights. You simply need some daylight in order to tell whether the foundation disappears in the skin or draws attention with a line at your jaw.
If none of the foundation shades look right, do not just apply the shade that looks most correct and hope to get the makeup to work after using powder and bronzer. Those products can make the finished look somewhat different, but they cannot totally adjust a foundation shade that looks too different from your own face color. It is better to keep the face foundation-free than to practice using a shade that forces you to learn how to make up for the wrong shade. When the shade looks right, everything else looks easier: concealer placement looks better, blush seems more natural, and powder does not need to be used to correct a bad shade match.
A good self test for a shade choice is to apply the shade only to half of the face. Blend it using a makeup sponge or with a foundation brush. Then stand away from the mirror. Check your jawline and the areas around your nose and at the lower half of your cheeks. The treated side looks better if the skin looks smoother, not covered. You can still see skin texture, but if your redness and uneven color tone look more even, the product is more likely to be the right shade and amount.