Mow the grass:  Chiggers like tall, moist grass.  If you keep it mowed short, they will leave for more pleasant accommodations.  It's really that simple.  Remember, you have to keep it mowed regularly.  If it gets high, they'll return.  You also have to mow ALL your grass.  If you have a ridge of high grass around a fence line, they'll get you as you walk by.

Flea Collar:  Sometimes it's not practicable to keep the grass mowed, or perhaps you're entering a field for the first time -- such as hiking.  You could use an insect repellent, but you'll be avoided by anyone in your vicinity, as you'll smell like DEET.  Wear a flea collar on each of your ankles.  Don't believe it?  Wear a flea collar on one ankle but not the other.  You'll get bites on the bare ankle, but none on the one with a collar.  Your friends may avoid you because they think you're strange, but it won't be because of the smell.  (Bark occasionally -- it'll really make them wonder.)