Physical barriers like window screens are best, but where even this do not work, try citronella candles or mosquito coils. Formerly, mosquito coils were made by mixing Chrysanthemum flowers and leaves with ground coconut shells as base. At present however, I think DEET is being used to make these coils. If you can't stand being ' smoked ' the whole night through, then steer clear of coils. If all else fails, stay inside your mosquito net.