If you are keeping up with the AI in tech, then I suggest you focus on improving your war style.
I consider there to be three basic types of successful offensive stacks. First is the very-early-game stack. Numbers are often pretty small-- 6 may be enough to take a capital, if you get them as early as possible. Axemen work, so can phalanx, quechua, and immortals.
Next type of stack is the siege+ stack. You know how to make siege weapons so you use them (preferably lots of them) to take down cultural defenses.
Next type of stack is the fast stack. You use units that have good strength and speed (knights and cavalry work) and you outnumber the enemy enough to kill whatever they defend with, without waiting for one-move-per-turn units to catch up. The enemy doesn't have much time to build reinforcements, and doesn't have time to move reinforcements from far away. You bring a large enough number of units that cultural defenses can't stop you.
A couple other basic strategies I follow are: try to get happiness resources. A warmongering empire always needs happy-resources-- they will allow you to increase your cities' population and also can be used to counter war-weariness.
If you have unhappy citizens, they do nothing useful and they eat food. Use slavery to lower your population (usually, rush-building something that kills off the number of non-working citizens plus one is the way to solve the problem). You'll need to use the slavery civic. Also, if your cities are ever working tiles like unimproved grassland (2 food, just enough to feed the person) consider using slavery to kill them off. (though it's often a bad idea to use slavery to kill just 1 population at a time).
People will tell you score means nothing, but really does (sort of) indicate how close you are to a domination/conquest/space-race victory because having the most tech/population/land is a huge help for those victories, and is also the bulk of your score. Some things that will help you to get a good score are building enough workers so that you can keep your population running good tiles settling places that allow you to work good tiles (food resources and happy resources) and capturing cities that allow you to work good tiles.
Early-on, special resource tiles that give you 4+ commerce are quite good, and so are tiles that give you a good amount (4/5 or more total) of food and production, like wheat/horse/iron/etc. Of course, iron, copper, and horses are also valuable for the military units they allow.
It's a good idea to pay attention to the obvious times when a particular building is worthwhile to build, and also to try to avoid certain building in certain cities. A city with a barracks and a forge, and not much potential to work tons of cottages/gem mines/sea coast tiles, should probably just avoid science and gold boost buildings, like library and bank. With a city that's mainly going to have cottages, you might want to avoid a barracks.
