If you are arriving to Paris by train from another country or from other cities in France, you will most likely be arriving at one of the largest European train station, Paris Gare du Nord.
It is a beautiful and rather impressive building.
There are several things to keep in mind to ensure you have positive experience.
Metro
Paris metro is very easy to use, it runs often, has frequent stops that cover most of the city. If your hotel is not within a walking distance from Gare du Nord, and you don't have much and heavy luggage, metro might be the best choice to get to your accommodation. Several metro lines have a stop at Gare du Nord. See Paris metro map or try Google maps.
You can buy tickets from vending machines or kiosks with personnel (often, but not always, English-speaking). Things tend to change, but sometimes machines accept only coins or credit cards (no paper bills). To avoid any issues, it is best to have coins, cards and paper bills at hand.
Please keep in mind that many stations in Paris metro do not have an elevator or escalator, and even if they do, some might not be operational.
Learn more about metro in Paris and types of the tickets for metro.
Taxi
The most important thing to know is to always take only official taxi to avoid being scammed. Follow the Taxi signs (not always clearly displayed, but they are there). Join the line, even if you are tempted to agree to a nice offer from someone approaching you at the station who is saying they are also an official taxi.
Uber
Uber is always an option. Similar to other countries, book online and the car will be there in minutes. Learn more.
Toilets at Gare Du Nord
Please note the toilets are for a fee (€0.70). There are free toilets in Eurostar area, if you travel by Eurostar.
Safety
As in any large city, be aware of your surroundings. Make sure your documents and money are secure from pickpocketing. Paris is a safe city, but Paris is also one of the most visited cities in the world, and that always attracts pickpockets.