Paris Warnings Or Dangers Tips by worldkiwi

Be prepared to queue for entry... Long Lines and Queues Review

Be prepared to queue for entry to major attractions. I had never come across anything like the queues I saw in Paris, but then it is the most visited city in the world apparently.
Going early to the attractions you want to see, seems to be standard advice and it makes sense to me. From my observations queues seem worse about the middle of the day.
Don't try and do too much in one day - you'll only get grumpy and stressed.

Crossing the road is a risky... Driving & Drivers Review

Crossing the road is a risky proposition in Paris. The best way (but by no means the safest) is at a crossing controlled by traffic lights. Be careful when accepting the green man's invitation however, as not every driver in Paris heeds a red light.
Pedestrian (zebra) crossings are a trap for the uninitiated! Parisians do not stop for pedestrians using these. Those on foot must give way to cars.
J-walking is just plain hair-raising, though by no means impossible. Don't attempt it on the Champs Elysee though!