Then what signify as "intelligently trading techs"?
You need to take the time and effort to learn how to be a
Tech broker. Here's a quick tutorial:
1. Research Alphabet, as it enables Tech trading and make contact with every Civ you possibly can, as early as you can.
2. Trade anything for anything, and with anyone, as long as its not totally ridiculous. Never, ever trade away Alphabet, since this would take the initiative from you. (Your rivals could just trade among themselves. As long as you monopolize on Alphabet all Tech brokering must go through you.)
3. Don't bother with researching all the early Stone Age and spiritual Techs and whatnot, if they don't give you immediate benefits. (Like enable you to harvest special resources.) Go for the more advanced stuff that your rivals will wanna trade for, and you'll get all the other stuff for free.
4. When the rest of the Civs finally get Alphabet you will already have a comfortable Tech lead allowing you to trade any new Tech you research for whatever anyone else has. This way you will have all available Techs, without having to research them yourself. Make sure to trade a new Tech to everyone when you decide to trade it to someone. (It would be prudent to wait until your rivals have something worthwhile to trade for, though.) Now you really need to start paying attention to what you are trading to whom, or you might just loose your Tech lead. (Especially if you're not doing that much on the research front yourself.)
As to trading resources you should always try to trade for all available luxury resources. This means that your cities can grow without discontent citizens, resulting in higher production, more

and better trade routes. It might be too expensive to buy luxuries, though...
And you should always sell
any surplus you have of your own. The food resources you can sell for whatever price, the luxury items should net you at least 5

per turn (initially, more later on), but wait until you can get a good price before granting a rival access to any strategic resources (that enable new and more effective units). You don't have to get the best deal immediately, but you should try to sell everything wholesale, because the

income per turn does add up! You will end up filthy rich very quickly.
Check what's available on the "market" every few turns (Foreign Advisor, F4) and cancel trades that aren't all that lucrative. Look how much

is available and what your rivals will buy, and sell the resources to the highest bidder! Repeat at intervals to always have the best possible deals in place.
Open Borders is an early priority with just about anyone because it will only give you benefits. Now you're pretty much playing as Tokugawa is programmed to, and he rarely gets ahead, now does he?
If you learn how to master all these trade techniques your game will be at another level altogether. Remember that it doesn't matter if your rivals benefit from trading with you, as long as you also benefit. The alternative would be that all the others are getting the benefits from trading, but not you. By being the most active trader you will always benefit the most from trade, so trade is a good thing.