Shading
Make sure your plants are well shaded on hot days to prevent scorch. The easiest way to do this is to apply netting or shade paint to the outside of the glass. Scorch is exacerbated if leaves are wet, so take care to water plants carefully.
Damping down
Damp down the greenhouse floor every morning on hot days to increase humidity. The plants will love this and it also helps to discourage red spider mite.
Tomatoes
Regularly pinch out any tomato sideshoots and tie the leading shoot to its support. Feed plants weekly with a high-potash tomato fertiliser, never letting them go short of water.
Cucumbers
Pinch out the tips of sideshoots to a couple of leaves beyond any developing fruits. Remember to pick any cucumbers regularly, as leaving old fruit on plants delays further flowering.