Placement of cities is key. Everyone knows to grab the river-hill-mountain spots but recognizing where the other good spots are is tricky. Don't hesitate to move your starting settler. Overlapping city/garrison damage spots at a chokepoint is awesome. Sometimes you want to settle on top of a lux. Sometimes you want to forward settle on even a grouchy neighbor. Sometimes one tile's difference in placement can make it so that all the spots 4 tiles away are crap. Plan where you want your next city is going to go whenever you place your current one. Wonders are a gamble and getting yoinked can take you right out of the game. The fail-gold from Great Library isn't even enough to buy a Library. That's why most discourage trying on the higher levels for anything early era except Oracle. Almost every other Wonder you can get the full benefit of when you conquer the guy who built it instead of building military. Check on other civs frequently to see how you compare. Being last in Military has consequences. If you don't start gaining ground in Literacy once the Renaissance begins your chance of winning starts looking bleak. Keep checking to see if any civ has redundant luxes you might need to trigger We Love the King days or fulfill City-State quests.