Here's my tips.
1) Make sure there are roads everywhere. For example, lets say there is an iron mine near a hill thats producing your civ iron. In order for all the cities to build iron based units (swordsmen, etc), there needs to be a road connecting from the mine to all cities. If you only have a road to 1 city, only that 1 city can use the iron. So make sure you build a spiderweb of roads connecting all cities from/to each other. Roads also increase trade, which puts the "coin" icon in the tile and it helps generate money.
2) If you do have an iron mine the enemy will destroy it as soon as they can, to stop you from producing iron type units. So make sure you place defensive units on the mine, like a swordsman/archer, and if you can (I haven't tried if you can do that) build a fortress on the mine, but it might actually remove the mine, its been awhile since I played, but if you can stack a fortress and defensive unit on the mine, do so. Also with horses, etc.
3) Make sure you have atleast 3 defensive units in a city. When the enemy attacks, they usually come with a huge force, you will need atleast 3 defensive units otherwise you will get wiped out soon. Also make sure you build city walls/castles to boost defensive strength.
4) Don't expand too quickly, as the cities haven't had time to build up its infrastructure, which will cause other cities to lose resources/money as its funneling money into new cities. The idea is to always try to have 1 or 2 cities in the "building up" stage at the most, once you get workers into the area, and the roads/improvements are made all around the city, then start expanding again. Never neglect workers/roads/tile improvements. If you don't have enough workers and have a ton of towns, the infrastructure/trade won't be good enough and your civ will go bankrupt.
5) If you plan to attack, and a city is defended by 6 units, you will need atleast 12 units to take it over.
6) Once you can, try to keep other civs happy, even if they demand you do stuff for free. Watch their disposition on the screen "Annoyed". Once you get a few civs which like you, make sure you get alliances with them. Other civs are getting into alliances with others. Later on if you have someone declare war on you, they pressure their friends to attack you as well. So sometimes you think you get a single war, only to have 3 other civs declare war on you as well. You have to have alliances yourself to help fight back, otherwise its just a matter of time before they will deplete you and win... So make sure you follow the diplomacy and don't be too greedy with others, make sure others like you and find alliances, coming to them after the war has started won't work.