I'm new to this post and am not sure how well known this stratagy might be. Spend your time on one branch of technology for a bit, then steal 2 technologies from a nation which was researching other branches for the cost of one steal. Do this by first beginning to research a technology you intend on stealing, then steal it before any research has gone into it. Once you successfully steal this, your researcher will ask you what to research next. Click on "What's the big picture?" When you do this, other technologies that that civ has will be in blue. Click on the one you want and you will have successfully stolen a second technology. It workes everytime, and I always get 2 technologies for the price of one.