I'll give you some basic tips:
This game is all about exponential growth so the most important room for improvement is almost always the first 50 turns or so. Learn the early game well and you will find that mid game you win no matter what until you get to the very high difficulty levels.
1: Worker is almost always the first thing you should build in your very first city.
2: The first thing you should tech is whatever tech allows your worker to improve your best potential food resource near your first city, (I.E.: Hunting if you have a deer, agriculture if you have a corn, animal husbandry if you have pigs). As your first city grows in population, try to have the worker improve all tiles it is working. Working unimproved tiles isn't good--if you're still working too many unimproved tiles, consider building a second, third, or fourth worker early game (you'll usually want about 4 workers by the time you get four cities).
3. Don't be afraid to chop extra forests for extra production to rush the construction of important things like extra workers, or settlers. This requires bronze working, a valuable early game technology.
4: Usually you want to get pottery relatively quickly and lay cottages down on riversides. This will give you enough commerce to expand your empire. If you don't have any riverside, you can run a specialist economy where you tech towards writing, and then build libraries in 2 or 3 cities, then run scientist specialists.