Unless you're on a salt-restricted diet, take an occasional salt water tablet or some salt solution when you've worked up a sweat. Avoid thermal shock. Acclimatize yourself gradually to warm weather. Treat yourself extra gently for those first critical two or three hot days. Vary your thermal environment.
Physical stress increases with exposure time in heat wave weather.
Try to get out of the heat for at least a few hours each day. Don't get too much sun. Sunburn makes the job of heat dissipation much more difficult. Know the heat syndrome symptoms and first aid.