Lombok is getting better in terms of hygiene and medical facilities but it still has a long way to go. You do not want to have a medical emergency here - getting off the island could take time. Play safe and make sure you have medical insurance before you come. Best to have insurance that will evacuate you if you get terribly sick or have a serious injury and need airlifted to Singapore or home. Here are a couple of other common sense points that should keep you in good shape and enjoying your visit.
Malaria does exist on Lombok but is generally not a problem. But IF you are sleeping in the open air, use mosquito repellent and a mosquito net.
A few other pointers. Drink plenty of fluids (water and fruit juices) to avoid dehydration. Drink bottled water ONLY. Even in hotels it is best not to drink straight from the tap. Ice in drinks, however, is not a problem. Use common sense when choosing a place to eat. Eat in established restaurants that are clean and well patronized. If you are dead set on trying the hawkers in the street stick to those not serving meats unless your system is already well adjusted.
If you are using prescription drugs bring a sufficient supply. Pharmacies (Apotiks) often can fill a prescription but the dosage may not be quite the same as your doctor has prescribed. Take prompt care of any cuts or burns - do not risk infection in this heat and humidity. If you are sleeping in the open air, use mosquito repellent and a mosquito net.