In Deity, you'll be technologically inferior to the AI for most of the game.
If you chase the south branch of the tech tree, you can achieve rough military tech parity with the AI three times: Warriors (the very beginning), Longswords, and Artillery
If you chase the middle of the tree, you'll be at parity with Warriors and possibly superior with Horsemen, but will have a rougher time after that if the Horsemen don't do enough damage.
If you chase the north of the tree or spread your teching evenly, you'll have a very rough time surviving.
A couple tips...don't be afraid of war. Being at peace with a Deity AI just means they are stockpiling units that will all come at once. If you go to war early, you'll be killing off their units a steady slow pace, which is MUCH easier.
Don't build a worker...the AIs start with them. Just wait in range of a hill or forest with a resource and run a warrior in when the worker moves there. There is a good chance you'll survive the counterattack and keep the worker, especially if you move another warrior into the AI territory at the same time to spread out the damage. The AI is not good at concentrating its fire.
Don't be afraid of burning a GG on a Citadel. You get more GGs in Deity, and you can afford it. A well-placed Citadel with a promoted unit backed up by a medic can hold off an army. Also, don't be afraid to pull back from the citadel when things get really bad. Defending the city behind it is more important. Take advantage of the 3 damage the Citadel will do to enemy units on or next to a Citadel. If you have a really bad meat grinder that multiple AIs are funneling through, drop another Citadel adjacent to the first. Stacked Citadel damage will completely obliterate multiple armies.
Take cities when you have a moment of tech parity. This requires preparing in advance, picking your targets, and being realistic about how much you can grab and what you can defend.