This article, written by two French students completing a summer internship in Hanoi, can be quite helpful. It includes a list of recommended spots in Hanoi, things to see, streets to explore, and good places to eat -- all sorted according to their respective locations. Note that the article was written in 2016; the prices for most of the products mentioned have changed a lot.
The Visitor Handbook by Viasm contains useful information on SIM cards, currency exchange, hospitals/medical centers, religious sites, restaurants, Vietnamese food, tours, and more.