N,N-diethyl-3-methylbenzamide (DEET) remains the standard and most effective.  There are a variety of mosquito repellents on the market both chemical and natural.  There is some experimentation to find which works the best for your body.  Also, rotating between several types helps.  Follow the manufacturer’s directions.  Product with Picaridin, and Oil of lemon-eucalyptus are also very effective.