Remove the grass with a spade by digging straight down several inches and peeling back the turf. You can use the spare sods to repair any gaps in the lawn.
If you don’t want to dig out the grass, you can smother the area with thick layers of newspaper. If you do this in early spring, it will be ready for planting in autumn.
Dig over the soil and add plenty of organic matter like well-rotted manure to bulk it up. Now you’re ready to plant it.
What you grow in your new border is entirely up to you, but here are a few tips. Check that the plants are happy in your soil and sunlight levels before you buy them. Give each plant space to grow into, so it doesn’t smother its neighbours. And plant some evergreen or woody structures that will look good in winter, otherwise your border will look barren once summer is over.