-.- they trade too damn quick for my taste. but after a while, u'll understand or at least able to predict their research pattern. SO in short: DO research those techs that u think they will not research.
Why? To exchange for other tech of course! I got off luckily a few times, getting a tech from research, trade it for another and used it to trade for another. So it's like I researched 3 for the price of 1! Having Scientific trade is great too! Freebie tech per Age.
Avoid dead end techs: Meaning, Music Theory and etc that branches to nowhere UNLESS other techs have been researched by the AI. Trade that for a better one.
Great Library makes it much more easier on the early stage. It allows you to focus on Monarchy / Republic without worring abt missing techs. Best thing: U DOn'T Need to trade techs till it becomes obsolete. U save money AND research time. It's still my fav Wonder since Civ I
A tip. Go for broke when u research. a deficit of 10-50 gpt is bearable. when 1 turn is left on your research, crank down the Science tax down to 10% it'll help u gain back your money (25%-50%) lost when researching.
Another way is to keep the AI Wayyyy behind you after you get G-Library. DO NOT Trade techs you have! . KEEP IT. and laugh at them as you focus on your teching. Trade only when you really need the Wonder / Resources.