Ideal general therapeutic dose: 2-5 grams/day. Nordic Naturals brand produces the highest quality products.
However, I would suggest obtaining your supplemental Omega-3 fatty acids from "Neptune" type Krill oil. The naturally occurring antioxidant content (Astaxanthin, Vitamin E, etc.) will retard rancidity, to which fish oil is particularly susceptible. (Fish oil consumption is known to drain Tocopherol stores in attempt to preserve the inherently unstable long-chain PUFA's.)
Additionally, the EPA/DHA contained is phospholipid (vs. triglyceride in fish) bound, resembling the structure of Omega-3's provided by animal brain tissue during our evolutionary past.
2 g/d would confer benefits similar--if not superior to--5 or more grams of fish oil, without the downsides.