Have no idea what "Extra" is?
Don't know enough about your game, level or the game you are playing to make specific suggestions in a vacuum. As far as I know your diplomacy and understanding of it could be poor. Are you new to the game?
Anyway, declining "offers" for trades does not result in any negative diplo, although accepting them "might" provide positive diplo. Declining "requests" or "demands" will result in negative diplo. Whether you decline a demand/request or not depends on your situation and relationship with that AI.
AIs never trade fairly. Their techs are always worth more than yours in trades.. However, keep in mind that they may offer a trade for you tech if they've already partially teched the tech they want, so the disparity may not be as large as you think. There are ways to figure this out if you know what to look for.
Anyway, I'd need to know much more about how you play the game to make further suggestions. I highly encourage you to spend time in the Strategy & Tips forum as well.
Oh, and some AIs are, as you probably know, simply much more aggressive or demand-y than others.
For example, Joao is a pretty swell guy. He's actually often liked by almost all AIs regardless of modifiers or peace-weights, except when religion starts factoring in. He's fairly easy to get pleased early on. However, he will almost always demand something from you early on after you meet him - tech or resource. If you accept his demand - that's it - you pretty much have a friend for the entire game, unless ofc, you want to kill him. Cathy on the other hand is very very demanding and untrustworthy, even if not as aggressive as some other AIs.
Extra is a mod that adds a bit of everything: new techs, new leaders, new leader traits, new civs, new civics, new resources, etc.
I've been playing civ4 for a few months, and civ5 a few months before that.
I was playing on a large map, with just three AIs, so having two of them suddenly wage war on me was instant rage quit material. We all had one one continent each, and the seas were high, so we didn't get to see each other until I discovered Astronomy.
I usually play peacefully. The only time I don't is for the sake of a gimmick (for example, "playing as the barbarians"). I'm pretty expansive, but I let my cities grow a little bit before putting their food towards settlers. I usually wonder-rush, so I have one city (my capital) rushing wonders, and other cities doing this and that. New ones work on the necessities: forges, granaries, work boats (if applicable), etc. Older ones might work on health/happiness buildings, wonders (on occasion, to give the capital a break so it can "upgrade"), or settlers, depending on what I feel is more pressing.
For the most part, I don't do much with the AI. I use to, but when I asked for something, what they wanted in return was not worth it. I find that the AI is too hard beyond Noble, but on Noble or lower, they're usually quite behind in tech, so all I ever asked for were resources. I also rarely accept open boarders; I always had a huge fear of civs marching their units into my territory and tearing me apart from the inside. I will think differently next time! I also thought that tribute demands were like bullying. You know, "give me your money or I'll hit you". I assumed that paying tribute would only encourage the AI to continue demanding, until I have nothing left. I just find it hard to trust, I guess. But if it works, I'll try it.
