1. Everything must be fresh, especially fish, vegetables and fruits. Don't buy many, buy enough for one meal. Each time. Tomorrow it will be fresh delivery on market.
2. Do not overboil. There are two main rules in cooking - 'less heat' (less flame under your bowl and inside your head =) and 'just enough' (long boiling spoils everything - taste and goodness)
3. DRY - Do not repeat yourself. Do not try to eat the same dishes day after day. You will spoil all your effort. Even a pure caviar diet will finish you in no time.
4. Eat local and seasonal fish and vegetables.
5. Learn from the poor. I learned from Nepali and Tibetan people in Hymalayas. They have very smart aproach to cooking.