Invest in some shade cloth or trellis – create shade for large pots to keep them out of the sun in hottest part of the day.
Protect new plants – cover or move pots to a shaded area to prevent sun scorch.
Keep pots cool again move pots to a cooler area.
Mulch borders and pots, providing mulch can help keep soil moist and cooler for longer.
Windbreaks, you do not need wind to damage your already vulnerable plants.
Keep up with weeding, thoses weeds will not stop even when its super hot, make sure they are not crowding the plants you want.
Pests are still about so keep vigilant.
Water early or late and not on leaves, this allows the water to soak in to the soil and not be evaporated by the heat.
Do not worry about brown/dry grass, grass is resilient and it will bounce back in no time.
Provide food for plants, just give your plants that extra boost with some plant food.
Keep yourself hydrated and cool, dont forget gardening is a physical activity dont forget to look after yourself.