Keep hydrated with water, juice, or iced tea (We are going to try cooling peppermint tea), try and get through 3-4 large water bottles a day!! Eating snacks that are high in water levels is good as well: cucumber, watermelon, oranges etc.!! And lots of ice-lollies; you can create your own so you know how much sugar will be in them!!
Take a cold (hot) water bottle to bed with you or an ice block wrapped in a t-towel. Dampen a t-towel and place it over a chair near to (not too close to) a room fan. This will reduce the temperature in the house.
Have a regular time outdoors in a shaded part of the garden or go for a walk through a woodland.
Keep some cooling peppermint body lotion in the fridge and apply throughout the day.
For all those younger buddies out there make drinks with ice-cubes. Fill a paddling pool in the garden. Or fill a plastic storage box and have some water fun indoors, this also reduces the temperature in the house!