There are many things that can cause areas in a garden to have dry soil, where an area might not get a lot of rain, have decreased rainfall due to shade or maybe have soil that doesn't retain water very well. If you have any of these situations, you might choose certain plants well suited to give them the best chance to grow.
Planting in dry soil
Dry soil in a garden can be caused by a range of different things such as a lot of sun, a lack of rain, too much shade, soil with a lot of sand/stones, or a combination of things. Plants may be suited to dry soil generally or prefer one of these things specifically.
When selecting plants for dry soil you can either use plants well suited or ones that need more moisture and maybe add something to the soil to help it retain moisture and/or water the area regularly. Also keep in mind a plant well suited to the dry soil you might get in the summer might not grow well in colder weather during the winter, so check if a plant suits all the different weather/conditions your garden might experience during all the seasons.
In the UK, the south generally gets more sun, so in areas like this you might use more plants suited to full sun. The soil in these full sun areas can be quite dry, so you might use plants suited to the combination of dry soil and full sun. But if other things cause it to have more moisture, such as being nearby a pond or you watering the soil regularly yourself, you might choose full sun plants that grow best with more moisture. The south east of the UK generally gets less rain so the soil can be dryer.
When looking for plants suited to full sun and dry soil you may come across the phrase drought resistant or drought tolerant plants. The meaning of this can vary, but generally it refers to plants that can grow in particularly dry conditions, often caused by a lot of sun, so full sun/dry soil, or a period of decreased rainfall. If an area is particularly dry you might look into what common properties plants suited to full sun/dry soil have, for example they often have things like spiky leaves and or are scented.
A dry area that's shaded is another common combination, where you might use plants suited to dry shade. This can happen in areas like under trees, near a house or along your garden wall, where for trees the branches can decrease rainfall below them and the roots can use up soil moisture, and your house/garden walls can decrease nearby rainfall.
The soil composition in your garden can also affect dryness, where a lot of sand and/or stones can cause it to retain less moisture (and also other things like retaining less nutrients, so you might use a different compost for example that lasts longer in these conditions, and varying soil acidity).
Plants to use for dry soil
There's a wide range of plants that grow well in dry soil in the UK, so if you have particularly dry areas there's a good selection of plants you could use. Below we give some plants that are generally suited to dry soil in the UK. Keep in mind specific plant varieties may be more or less suited to dry soil.
Eremurus
Eremurus are hardy perennial flowers. Often called Foxtail lilies, they come in several varieties and grow vertically to around 1m-2m tall. They grow well in full sun and like well drained fairly dry soil.
Lavender
Lavender are evergreen shrubs. They come in a range of varieties/colours/sizes/hardiness, where you can plant them in your garden or just plant one in a pot. They grow well in full sun, like well drained dry soil and certain varieties can help attract wildlife.
Melianthus major
Melianthus major are tender (not hardy) evergreen shrubs (you can also grow them like perennial flowers). They prefer areas sheltered from wind and aren't very resistant to colder weather. They grow well in full sun and like well drained dry soil.
Verbascum
Verbascum are hardy perennial/biennial flowers. There's a wide range of varieties, some perennial and some biennial, they come in several colours and certain varieties are better suited to growing in the garden. They can help attract wildlife and grow well in full sun/well drained soil. They prefer some moisture in the soil, but are also fairly tolerant of drier soil.