Taking omega-3 supplements is fine, and so is eating fatty fish a couple of times per week. One of the best sources is mercury-free distilled DHA/EPA oil. It should be kept in the fridge because omega-3 fats are extremely sensitive to heat, light and air. This is why a lot of the capsules you pick up from the shelf won’t be much use.
Green tea contains quite a lot of caffeine, which is best avoided for as long as possible. You can buy green tea extract in capsule form that contains all the goodness of the tea with none of the caffeine though.