I thought that such a topic will be a welcomed addition, so please post your insights here.
Anyway, here's my hints - when playing as Human:
- You will receive a bonus to others' relations because you have the Super Diplomat ability.
- You will receive a bonus too if others are in war with someone, get them as the game begins, it's easy with Super Diplomat. Everibody in the game must be in war with somebody, or he'll turn to you.
- Fulfill other's requests, except for planets, this warms a relation.
- Choose Neutral responses and the Alignment always, this improve relations with Neutrals, but keep the Goods and Evils indifferent.
- The treaties are extremely important. You can get even double the sums of on your income or research. Make the treaties with neighbors as their bonus offsets the diplomacy hit because of close borders and influence.
- Research quickly Sensors and get Eyes of the Universe for ship movement and the huge sensor.
- Research Master Trade and build Galactic Bazaar - what you offer in diplomacy will have 50% more value. Master Trade also unlocks Economic Capital which is better to build one the home planet - it has the most population.
- Research Total Majesty and build Spin Control Center. Later,when you build Huge ships (I never build anyhing but Huge), they'll apear 5 times stronger and the relations will warm up because of the military strength.
- It isn't necesary to research always, just keep an eye of the offers in the Diplomacy.You can get very good deals with the latest weapons and defense.A percent 75% bought and 25% researched sounds fair.
- Send a freighter to every civilization - it's a bonus to diplomacy.
- If you want, you can send the rest of freighters to the nearest neighbor and set these 4 economy starbases filled with freighter modules.
- Never sell to the AI Diplomacy or the Alliance techs (or even maybe Influence ones).
- Control as many resurses as possible. Get a constructor to every resurce to wait it's destruction -won't take too long -or use the gift a ship trick to speed the process.
- Normally the game ends with a Diplomatic victory, everybody will get Close, but you can achieve a Influence victory by building Starbases or a Conquest victory.
- In the later case, the choose of the 30% Defence in the Race creation screen and 1-2 Military Resurses is invaluable to obtain the known 75% Defense per ship from the total Offense of the enemy fleet - which makes the ship almost indestructible. It's enough to take planets defended by one ship at the time; when you see a fleet, run away.