- Change your culture every era to take advantage of the increasingly powerful perks and buildings/units. The perk you see at the top of the culture's description stays with you the whole game. Just make sure you build the iconic building in your cities before you switch.
- Unlike Civ the majority of the way you are going to get resources is by claiming preset territory with outposts and then linking those outposts to your cities. This will also allow you to build districts in the area covered by the outpost.
- Shared constructions are shared for a reason, you can split the work of building religious sites and wonders between cities and get them up very fast.
- To take down a outpost or city you should ransack it with an army, which will clear its tile.
- You can take down other players' outposts without a declared war so long as they are not linked to a city (dashed border line rather than solid is unlinked). This will of course make them hate you.
- 80 war enthusiasm is the breaking point for a formal war, keep your enemies under this and you will be safe. They rarely declare surprise wars, at least so far as Very Hard difficulty.
- To force a formal war, go to the grievances menu and push for one they won't accept. This will give you a ticking increase in war enthusiasm that will eventually hit the required mark. If you don't have a grievance then push for an extreme diplomatic tie and then make their refusal your grievance.
- Don't expect too much out of a single war. You'll probably gain a couple cities, but you won't be able to wipe out an enemy entirely unless you go to war with them several times, because you buy spoils with points during the peace talks and you'll end up handing back over most of what you take, even if you annihilate them. This can work in your favor too, though, if you lose the war.
- In battle, take advantage of terrain, especially once you start getting into the gunpowder age. Guns can't shoot through your own units if you have two rows of them, but if they are on different elevations then you are fine.
- Alliances are more for economic ties, and should be considered just an extreme nonaggression pact. Don't expect them to come to your aid in a war, but also don't be afraid to ally yourself with everyone you can.
- City stability doesn't really start becoming a problem until below 50%, but still be careful not to queue up too many districts at once.
- Don't neglect non-district improvements, especially the ones that increase the output of workers in the districts. Why build one more farm for +4 food when you can make the improvment that gives the six you already have +2 food.
- It is sometimes cheaper to buyout a neutral citystate than it is to raise your own.
- Cavalry can't go over city walls. Bear that in mind if your neighbor goes for Huns.
- Don't give up if you start falling behind. Every game I have won has started with me being in fifth place in score, and then exploding upwards when I got to the higher technology tiers.