Most of the time 60%-70%, never below 50% -- except for a handful of turns when I needed money to make Bersekers out of my old city raider Axemen.
I quite often go down to 20-0%. Alot of the games I play I hover around 20% most of the early game and it starts to pick up at around Cannon (and after a few holy shrines) as I start to get more income comming in. It then settles at around 40-60%. I dunno, more cities with lower tech percentage vs a higher tech percentage but a slower expansion rate? I prefer the former although it can get hair raising when you are at 10%, -20 gold per turn and you
start a war with your neighbour inorder to expand further. It works though! If you stick at it and develop what you conquer. Maturing the cottages takes a while as does developing the shrines, but for a conqueror, getting Isabella's shrine mid game is like an oasis in a desert
It's the AI's demands in tech-trading that really makes things difficult. Some trades I simply refuse. As when they want several expensive techs in exchange for one. Sometimes it's just ridiculous, and I won't do it. Some leaders are worse than others.
That annoys me too. I wont agree with most of the trades either. I tend to play the game with this idea of not expecting much from the AI's. I tend to focus on building my economy and being totally self sufficient when it comes to research. I have found the AI to be rather eager to trade resources for gold per turn though, even to the point where you can keep cancelling them after 10 turns and raise the costs as they get more gold per turn to trade - can build a nice income that way to support an expanding empire. On that note, with a big empire, I generally have quite a lot of resources for trade too.
When you're interested in doing so, try to play a game where you continue to expand. Take over a neighbour. Consolidated it by building the cities and developing the land and continue expansion to infinity. There is a point where the slider just balances out and a huge, fast expanding empire (that is being developed as well

) supports itself while teching very fast - at about 40% I think - and with a big empire, I can catch up rather quickly. I think this has to do with the pace at which cottages grow, vs the cost of civic/city maintanence. But in the begining, I usually end up deficit spending at around 20-30% (clinging to the percentage rate with -20 to -40 gold per turn) and then conquer as a means of putting gold into the treasury by pillaging and capturing cities.
My GOTM3 (I think it was - the one with Tokugawa (my first Monarch game whereas I usually play Noble)), I just expanded with the idea that expansion would save my butt. It did! I was fighting Elizabeth's Musketmen and Granaiders with Samurai and Catapults, but by the time I finished her and Gandhi, I had caught up in tech and was (if I can recall), one turn away from Artillery. I think at some point in the game I was clinging to a 20% research slider while deficit spending and I just gritted my teeth and kept on expanding. For a Noble player, that was a big thing for me to do on Monarch. Mind you, I had nothing to loose anyway and I ended up with just under 80K for a dommination win
... I learned a lot about expansion in that game and the illusion that a low research slider, deficit spending and going to war in such a state is not nessecerily a bad thing.
edit: noticed your thread name has been changed

Man this new posting system is cool!