1) Sent 4 tanks and 4 infantries to Isabella's domain, thinking it would be sufficient to take over her entire primitive empire. Next turn -> Isabella sent 50+ conquisidors at me.
Yeah, the Civ4 rule of thumb is, "spearman beats a tank may seem ridiculous, but 50 spearmen beats a tank is a guaranteed WIN!" You have to plan around that.
2) Never used siege to take down cultural defenses, thinking 1 rifleman should be sufficient in taking on 3 longbowmen with city defense II
Use spies. They die less often.
3) Start a nuke war with 3 ICBM (luckily, it was during the vanilla tutorial game with a pre-astronomy Gandhi)
It's usually over in my games, before nukes. I'm totally clueless on nuke strategy.
4) Tried to out-tech the A.I. peacefully in Prince and avoided any early wars before rifles
There *can* be some advantage to avoiding early war, and hear me out with all the IFS okay, there are important caveats not to disregard here:
a. IF... you got a huge amount of land that you REXed into in the opening game and your slider is still pretty damn low by mid-game.
b. IF... you already did an early war or rush and crashed the economy so bad you still need to recover.
c. IF... you got DoWed early and it took desperate measures and unnatural acts to fight off the aggro civ and regain the cities you lost.
d. IF... for whatever OTHER reason your cities lack a reasonable array of infrastructure to optimize their unit output. I'm not talking about city walls in a back city here, I mean like marketplaces where they give resource happy bonuses so you can grow and work more tiles, etc.
e. THEN... (note all the previous IFs first here)... then it can be more prudent to improve the condition of your war machine before going to war. My general rule is that there has to be at least 2 cities running at optimal military output for their tile yields and potential bonuses, etc. Other cities can still be working on infrastructure if (there's that "if" again) there are some older units previously built up for potential early war that can still be used in conjunction with the modern units for future upgrades or "collateral damage sponging".
5) Built armies consisted of 4-5 units
Some stacks only need 4-5. I've gone to war with huge stacks sometimes only to find on average 3 defenders in a very long series of cities, not uncommon with a tech whore like Mansa. ESPECIALLY along a coast where naval units can bombard the city defense (or late game if air units can do the job) then it's more optimal cost-wise to send a stack in at just the amount of city raid units needed to take the city. And if earlier on you launched the war with a stack of 50+, later on in the war it's better to split them out into multiple stacks to seize AI cities in parallel. A fast war is a successful war. Gives more time to fight more wars, elsewhere.
6) Refused every demand of A.I.
Unreasonable demands make sense to refuse most of the time. Monty wants Rifling for free. He's on your border. What are the chances he WON'T use it against you? Do you feel lucky?
7) Never cared about religion thinking they are all just thematic stuff
Religion has benefits but spreading it has prohibitive costs. I've blasted over 10 missionaries at a city before as it refused each time to spread the religion there. Those hammers could have converted to coins in WEALTH those turns and drawn more benefit than even the game-long benefit of 1 coin/turn with a shrine.
Shrine-whoring is only slightly less n00bish than wonder-whoring, when you think about it. Especially if you're trying to throw your beakers into religion techs instead of techs that matter, and GPPs into prophets instead of scientists and engineers.
8) Never used organized religion because free religion's obviously the best
Early game the tradeoff is the diplomatic hit if you're running the "wrong" religion, as well as the potential tradeoff of the fact that if it's someone else's shrine, you have to give that AI a 1 coin per turn bonus for each city's 25% hammer bonus, which isn't enough to make it "not" worth it, but it's a slight bit of rain on the parade to consider. When it's Monty coins it'll mean a few extra knights in his renaissance stack against you; when it's Mansa it'll mean he gets even MORE run-away-techish. Drink responsibly (the OR kool-aid). Flipside is, if it's an Apostolic Palace religion, there's no excuse in the world NOT to spread it, for the votes (those Palace votes for you to give away a city or stop a successful war, are KILLER!) And if you have to universally spread that religion, might as well get the hammer boost for it.
Mid-to-late-game, that extra 10% research comes in handy after a Liberalism slingshot and suicide Internetting, to "catch up" on tech and then use superior human strategizing and city output, better core war machine, to go own. It can sometimes mean the difference between attacking Rifleman cities with other Riflemen, or, ...infantry.
9) Built roads over every tile in early game thinking a tile's yield can only be received if there's a road in it
I used to think in Civ2 terms that the road would give a commerce bonus, lol.
10) Built farms whenever I could
Would have made you a natural for SE's hehe.
11) Never razed/gifted any city regardless of how useless they are
That was a hard habit for me to kick too. "If the AI saw a reason to build it there, it had to be worth it!" My answer to myself from a more experienced player's viewpoint: "NO". Burn baby burn, or gift baby gift (tundra, etc.)
Exception: early game sometimes the AI have a secret knowledge that something key is there like the only oil on the land mass. I hold off on razing in those cases, and gift (or liberate) later if they truly ARE worthless.
12) Never used state property because American game producers would generally make communism very repressive and useless
Hopefully if you're sitting on 10+ mining resources and 10+ sushi tiles, you don't flip to SP?
13) Never took Monty's threats seriously when he was a neighbour
LOL... uhm... yeah. Been there done that. With Aggro AIs you're lucky if they even bother to make a threat, they just saddle up and ROMP.
.... and if a rival built any of them I would take it personally 
and focus on razing their wonder city
Then I read something about gifting missionaries.... "ohhhh so it only stops OTHER CIVS from spreading it to me."
