Install a water butt. You will be grateful for hundreds of liters of free natural rainwater to keep your plants and lawn hydrated.
Use mulch around your plants, this stops the soil becoming dry in the first place and decreases evaporation on warm days.
Reseach drought tolerant plants, its good to have a few plants in the garden that dont require regular watering. Some examples are :- Echinacea, Ceanothus, Geranium and Red hot poker.
Lawns: It can be difficult keeping a lawn green in the summer months try raising your cut height this will keep some extra moisture in also reducing the frequency of mowing can help protect your lawn fro drying out.
With watering little and often doesn't always do the job as the water evaporates and only reaches the top level of soil which encourages the roots to grow upwards. A good soak every 7-10 days is more effective as the water travels deeper in to the soil saturating the ground.