It depends what you are using it for and how you plan to move forward.
If you are a shift worker or have chronic fatigue syndrome you are going to want to manage for long term effects, you'll be taking it up to 5 times a week (always take a couple of days off) and you want to get away with the minimal dose that will keep you awake, that's going to be 200mg for most people but 400mg is possible after a month of usage. taking more than this is serious business, even with a relatively benign drug like moda, make sure you have the medical history for this especially cardio health and monitor closely.
if you are taking moda for an exam or project a 1/2 (100 mg) will get you through a day if you don't eat much; a full 200 mg is ok, don't do more without an a.d.d. diagnosis.
whatever you do stay away from caffeine and other stimulants.