Remember to fleet save! This is the process of sending your fleet out for an extended period of time so it will not get destroyed. Many experienced players will send a massive amount of ships to destroy a smaller fleet and thereby harvest the debris field.
Be Balanced: Ogame is about balance. Whether you are a fleeter, miner or a turtle, it is best to have a balanced gameplay style. Defenses can protect a miner's resources, mines can help you build more ships, and fleets can sometimes work more efficiently than defenses.