How do you avoid or reduce the side effects of antiepileptic drugs?

Close follow up. Take as prescribed. Take lowest effective dose. Do not make changes without consulting md. Have blood work when suggested. If medication prescribed for other medical problems, check with neurologist and pharmacist for possible drug interactions. Take vitamins if suggested by md. Always be sure that you still need the medication, in the first place.
Trial and error. Some of the newer drugs have less adverse effects. Perhaps best tolerated is lamictal, but maybe vimpat (lacosamide). Need to work closely with your doctor. If too many side effects, maybe could benefit from vagal nerve stimulator device.
See below. Follow your doctor's advise. Routine testing will detect side effect early. Not everybody gets side effect mentioned in the literature. Side effects are weighted against advantage. Each anti epileptic is different for side effect to an individual.