Strategies depend on what version of the game you have, and your playstyle may not fit every strategy.
If you do not have the expansion, I would recommend going to the War Academy here at CFC and forming your own strategy with the advice you find in the articles there.
If you do have the expansion, you will find conflicting advice from many different places, as the "meta" has yet to settle. Furthermore, the game seems better balanced so that each strategy is situational, and no one strategy is over-powered and optimal in all scenarios.
This game is about opportunity costs, as no decision ever gives you a straight-up penalty. What you lose from choosing a certain social policy, prioritizing a tech, building a building, promoting a unit, etc. is not choosing something else. And this applies across categories as well. By choosing research (growth, libraries), you are not choosing units (production, gold) because high food tiles will not also have high production or gold, and constructing science buildings means you aren't making units.
So what the game comes down to is choosing exactly enough in a category so you still have effort to spend on others, and not neglect them. If you are going for a science win, you do not need to much culture, but you certainly want enough to fill out Rationalism (and probably Liberty/Tradition). If you have any more culture than that, you probably didn't build enough units to defend yourself, or you have less science (and thus lose an important wonder).
So obviously the hard part is determining just how much of anything you can afford. That will only come through practice. Take all specific advice you find with a grain of salt. Most importantly, have fun. Don't use a strategy if you don't like playing that way, as that defeats the whole point of playing the game. You don't need to play perfectly to have fun. Besides, that's what the difficulty levels are for, so you will always have a challenge no matter how you play.
