It can be hard to trade, Master Shake, and very often the AIs will refuse to trade with you, even causing you to fall behind a tech or two. Here is what I find works:
Research on the lowest science rate possible but still research a tech. So, for example, don't put it at x% if it says Iron Working (-) but put it at y% so it says Iron Working - 39 turns. That should bring you some gpt.
Then make the diplomatic "rounds" every two or three turns. If you see an AI has a tech and you have something to trade, offer it. If they will accept, don't make the trade just yet! Remember that you can trade with that Civ, and then check the others for the best deal on that tech, and trade for the best deal.
The other trick I use is to make multiple trades. Lets say that you have Masonry, while one AI has Pottery and doesn't have Masonry, and the other AI has Warrior Code and Alphabet and doesn't have Masonry and Pottery. Do you see what you can do here? You trade Masonry for Pottery to AI 1, and then trade Pottery and Masonry for Code and Alphabet to AI 2. By doing this you manage to take one tech and get three out of them.
So, in summary, try to remember these rules:
1) If you trade a tech to an AI, they will most likely trade it to other Civs the next turn, so try to monopolize all deals on that tech.
2) Check around for the best deal.
3) Trade techs you trade for, and look for multiple-trade chains (trade one tech for a second, and use the second to get a third).
4) Don't be afraid to trade gold and/gpt for a tech. As long as you turn around and trade this tech to other Civs, you can most likely recuperate your investment (although its not guarenteed, since the price of a tech deflates each time another Civ gets it).
Once I learned these, they became instinct.
