Well, I use a shameless tactic which works for advancing very fast in science. The game is on deity, the AI are much ahead so I focus on one city, take it, get the technology after conquest, then put my units nearby, AI takes it back (most often with a single unit, is AI you know...), I attack again and get a second technology and so on. On big cities works a couple of times until the population is too low to get a full tech. Once you have enough canons and with surround option + pick some hill with forest on is not that hard. Thanks for civics option, indeed the one which bans the corporations put my cities back and they rock now.
Also I play with unlimited experience from animals/barbs so I use a good army early game to create many generals, which I join to the same city again and again, so I have a city now which gives 150 experience (yeah, 70 generals) to every new unit, thats almost invincible if you pay attention