I usually play 18 civ emporer, and I win the techrace in 90% of my games (the other 10% I lose altogether after 10 AIs declare war on the same turn...).
A Few things that might help:
Try to have at least 3-4 science cities, they should have access to at least 1 food ressource and a lot of grassland/floodplains. Cottage them early and almost entirely. A Few mines early to build the needed buildings, turn them into windmills later. They should all have library, university and academy as soon as possible.
After the initial workertechs, start researching aethics (unless you have a special strategy in mind, like praetorian rush). You will always be the first one to have it, and you can trade it around like mad (it has low priority for the AI). Now get polytheism and literature and build the great library in your capital. It is the only wonder I am addicted to, because it gives you mass Great-scientist points as well as a nice number of basic-beakers, that will receive the bonus from libs/unis/academies. In my last game, the science output of my capital went from 440 to 370 the turn the great library got obsolete.
After literature, beeline to civil service and use bureaucracy, your capital should be the first city to get an academy. Also try building oxford here later. From here on, you can directly go after liberalism, starting with paper. Might consider Sankore when you plan on keeping a religion and not using free religion, especially when you use AP-religion (in that scenario, monasteries give 2

, 2

, 2

and 10%

). Then education, immediately starting universities. You need to plan ahead on the numbers to get Oxford fast. Then philosophy if you cant trade for it and liberalism.
Generally, getting techs early that the AI will usually get late will lead to great trading opportunities. Just dont trade techs away when you plan on a wonder , and dont give important military stuff to your neighbours. And if you can choose, trade with the AIs that are further behind, not with techmonsters.
Also, try to run representation as early as possible, the beakers you receive from your specialists will also get the %

from buildings and make a difference. But dont force the pyramids if you dont have stone, that may throw you behind.
Once you have the academies built in your science cities, every subsequent great scientist should settle in your capital.
At higher diffculties you will be way back in techs right as the game starts, and playing catch up. If you did it right, you will be slightly ahead at liberalism, and from here on the AI cant stop you. In my current game im doing 1900

/ turn after 330 turns on epic, and Im playing with tanks vs riflemen
