For tech development, I typically see what the AI's are researching, and then follow up one or two paths in a focus to trade to the AI. Odds are they will spread their research a bit, allowing you to trade your higher level techs in one field for many basic techs across the other fields. The diplomacy branch is good for this, as it allows for you to get better deals. Otherwise, just make sure you don't focus on the same weapon and defense, as you would be more reluctant to trade the AI laser defenses if that is your only weapon platform.