Take good walking shoes and literally, get lost. It's too big over a short trip to really see everything and there is plenty to see. Yet the beauty of Paris is that there is quite a lot to see and so many wonderful neighborhoods to get lost in. My advice would be to pick 2 or 3 areas or things to do/see and take your time to appreciate it. Moreover, get rest in order to be able to wander the streets at night - even consider a touristy night cruise/dinner on the Seine. It's beautiful at night.
Avoid fast food or chain restaurants, I wouldn't even really go with tripadvisor etc. - just wander through a neighborhood and go to a bistro that looks to have happy customers. Just remember the French are fairly regimented about meal times, you start looking at 2pm for lunch and you can forget it