Make drills exactly like the lettuces. If you’re going to pick the leaves early when they are small then you don’t need to thin them out, but if you want larger leaves then don’t pack them too close – at least 7.5cm apart. Good air circulation will prevent mildew, which is a common problem with spinach.
Gently cover them with a rake. Spinach will need protection after October with a cloche, fleece, or cold box, and you’ll need to keep them well-watered when there’s no rain.