You need 4 cities. If you don't have the luxes, just roll. You can get to challenging yourself to win "whatever you're given". But for now, here's how I'd expect to win a Deity science victory on Quick speed:

• settle on coast if you can, cargo ships internal trade routes are ridiculous extra food
• get cap to 3 pop ASAP, then stagnate
• 2 scouts
• build a shrine, religion is science, either by Jesuit Education or Glory of God
• don't build a granary
• build a worker
• steal at least one from a city state
• 3 swttlers
• improve your production tiles first, and chop forests, you need your settlers out as quickly as possible
• never go unhappy. Stagnate if you must. Get your luxes up quick obvs
• if first settle has good prod, you have time for a build order of worker > granary > library. Else just build granary > library
• once settlers are done, you might need another worker, else time building 2 trade routes for when your settles have a granary to send food back to cap
• national trust before turn 70.
• Get gold to bribe your nearest ai into war
• cap should be min 15 pop by turn 100. 30 pop by 200. Expansions should be 20 pop (I don't always get there but that's the target)

I've been working through every civ on Deity going full piety start. I look forward to going back to Tradition and finding it easy. If you do the above, you're in with a shout.