Diplomacy Tips or Strategies?

I start small with a 5% trade and slowly go up, that way I seldom get refused a treaty.

the minimium non agresion clause is also a fiarly sure thing

I don't know the actual mechanics so I might be wrong, but..

If you avoid enemy empire systems as soon as you come across them, and immediately offer non-aggression pacts, they never seem to refuse.

Early on, the top 3 treaty priorities are (to me anyway) non-aggression, trade, and immigration, in no particular order.

I'm pretty sure enemy empires won't ever accept 'unfair' treaties, but the AI is pretty bad at figuring out what 'unfair' treaties are, so you can negotiate around that.

I can't honestly remember if the AI pays any attention to what it knows about your empire when it negotiates treaties. It'd make sense if it does, but I doubt it.

You should, though, so start spying (not sabotaging, spying) so you know what your enemy's capable of. When you know, start tailoring a treaty preventing it from using it's nasty tech against you. You'll either have to give up your own ability to do the same, or offer other things (medical, repair and resupply services are always in demand it seems, and of no real consequence to you).

Same principle applies to getting what you want. Offer services you can afford to offer, or promise not to do things you couldn't do anyway, in return for what you need.

Breaking treaties is a bad idea. It instantly makes your former treaty partner hostile to you, so unless you're about to declare war on the empire, it's worth your time to re-negotiate the treaty elements instead - even if it takes 10-15 turns (which it typically does).

While treaties does seem to endear your partners to you, I think it's a one-time-only bonus to their attitude, so counter-intuitive as it seems, treaty partners won't warm up to more elaborate, and useful treaties over time.
Slowly increasing the magnitude of treaty elements is still possible, but you'll typically have to throw in free popcorn before they'll accept the new terms (by popcorn I mean stuff like "I swear I won't virus bomb billions of your pathetic species, and of course I need to promise you that since 15% of my income depends on you xeno scum not dying..."). Yes, it's silly. But it works.

By the way, sabotaging planets (which frequently starts plagues and is just as effective as actual bombing), doesn't appear to be a violation of the virus bomb thing. I'm not sure if massive sabotage operations will make a treaty partner call off the treaty, but it hasn't happened to me yet, and I'm quite fond of crippling enemies with sabotage. If they catch your spies though, they will get a bit pissy.

Really, diplomacy is so opaque I don't think it's even worth strategizing. Every game I have ever played is exactly the same(balance mod). All the enemy empires are so eager to get into a trade or at least non-aggression treaty that nothing is ever refused unless you out-right attack one of them, even then...

I've never seen them break the treaties either. So MY strategy would be to attack a few empires right at the beginning. Otherwise it will be a very dull, very long endeavour with no pay-off.

If you wait to attack them it's basically like cheating as you can pretty much coast along till everythings researched. Wheres the fun in that?

I have a question that goes along with this topic, what is actually traded with the trade %'s? I have signed many trade treaties and I can see we are trading 10.5% up to 20%, but I have no idea what is actually being traded, or what benefit I am getting from this trade.

Currently because the ai is so undeveloped, I find diplomacy just a delay until I destroy them. This may play a more important role as the ai is actually developed more. Have you ever had the ai attempt to trade technologies with you? I looked and the amount of things that can be traded between empires is huge, but the ai never attempts to trade (only treaties that force you to have no intelligence/research/etc.)

AFAIK the percentage represents the % of ressources of the less productive empire that will be "created from nowhere" and given to both empires, the ressources being minerals, organics and radioactives.

I've never seen the AI make trades, only treaties, and never any "No ..." treaties so far IIRC. I think they use all the other treaty options except mutual defense.

You shouldn't use the treaties to keep the AI at peace, otherwise they will never attack you and you'll be for a very long and boring game... make at least one neighboring enemy!

I frequently receive treaty proposals that contain empty parameters. If I go throught the list they will somtimes have the option for share resupply, but none of the check boxes are selected. Now I have never had one of these treaties be entirely empty, but just some of the treaty details are "empty".

I do really think this is a bug since playing my latest 1.35 game almost every treaty offer had an empty parameter.

I had those sometimes too...

I've seen plenty of "No" treaties, blocking anything from research to spying, and the same goes for military alliances. I can't be certain (since I wouldn't know what to make of the game files, even if I knew how to read them), but I'm as close to certain as can be that AI players frequently - possibly always - make military alliances, no research alliances, no spying alliances, and similar silly things.

Since the AI won't break alliances on it's own - or at least, I haven't see it do it - it's a good idea to ban the AIs from having treaties with others. You can always break your treaties once the fighting starts.

EDIT: "Blank" treaty clauses don't count. Given the ambigous AI replies to being under attack and the like, it's easy to get confused, but a few determined violations of "blank" treaty elements should convince you it's a bug. Convinced me anyway

I think the best way to play is to try to play with only one or two allies and just refuse treaties from the rest. One actual fun goal for diplomacy though is to try for the whole alliance thing.

Since alliance right now is an excusive treaty with one empire you can only break but not change, that is probably a good way to not be tempted to befriend everyone in the galaxy...