There are a lot of good posts about openings, but in the most general strokes:
- make sure you work improved tiles for every city all the time. This means you need one worker per city for a good long while.
- population is the basis of everything, production, culture and most importantly science. Make growth in early game a priority
- (since BNW) make sure you don't go broke early game cause of units/buildings.
You might say... I know this! But it is the fundamental basis for winning the game. Your strategy should be aimed at succeeding in doing the above.
Personally i always enjoyed tall empires and therefor the Tradition tree. Don't bother with the very first wonders. I have seen friends go completely broke cause they build the pyramids, and went into -gpt cause of the workers and still lag further cause they didn't prioritize growth (but hammers to build said wonder...) Your build order should start with a scout in general. Scouting gives gold, science (through the meeting of neighbors) and information where to settle. I normally tech towards theology and education while disregarding the bottom half of the tree for a long time. Build the National College quickly! By the time you get education you should be able to build a university quickly (or buy it) and have pop to use as specialists. Typically i also build the writers guild in my capital so i have 4 specialists. From there anything goes, you got your basis covered. Depending on the aggression level i normally tech towards Crossbows then, but i also found that since BNW that isn't always needed.
Hope it helps!