During the last 12 months, I've had the chance to travel quite a lot (The Netherlands, Belgium, UK, US, South Korea, Hong-Kong, Japan). Thanks to these experiences, I have gathered quite a few pieces of advice regarding how to prepare, organization, etc. I'll keep updating this article as I travel.

Before departing

Carry-on: make sure you have a few clothes in the cabin, don't pack everything into the hold luggage.

Make sure you have VLC installed on your Android phone to watch movies and/or TV series. VLC in more convient for that it supports a wider variety of formats and allows one to add subtitles. Also, you should have an offline access to what you intend to watch on your mobile phone or laptop, along with subtitles.

You may want an Internet access. Most airlines will offer Wifi for a few dollars, however if you have a VPN set up somewhere in the world you might be able to access the Internet for free using it. More importantly, even though you decide to pay, you may want to protect your privacy. How so?

It is better to know your VPN's IP, it makes things easier.
OpenVPN is handy, and there's an Android app for that (free!)
The VPN server should be reachable on ports 80, 443, 53 (DNS) or any other random one. Indeed, those are the ports less likely to be blocked. 53 is the preferred if you want to reach your VPN without paying.

Last but not least, take outlet adapters (practically all planes are US outlets compatible). In addition, a USB to AC converter would come very handy, as there are more often USB outlets than AC power plugs. This way you can use a laptop.

Before ending this ending, very few people know that but French citizens can get the taxes they paid back if they miss their flight or if it gets cancelled. Source: Peut-on se faire rembourser les taxes si on rate ou annule son voyage en avion ?

General advice for travelers

Plan two activities per day TOPS, if you want to enjoy them as much as possible and avoid being in a rush all the time
Bringing little gifts from your home country to your Airbnb hosts is always a good idea and will please them
Plan you trip in advance and thoroughly, and make that plan available to everyone in your group so that no one has to worry about anything

Don't get lost

Here are two great Android apps that you can use for free to find routes and points of interests in most cities in the world.

Google Maps, with the "Offline" feature. It allows you to download maps so that you can use them offline (it does not work in a few countries though, those that do not let Google access their maps, such as South Korea). This app is pre-installed on Android devices.
OsmAnd, available on the Google Play Store. It uses OpenStreetMap's data so it is basically available everywhere, thanks to users' contributions. Likewise, it has offline features which provide a great level of details.

Travels: tips and tricks

Before departing

General advice for travelers

Don't get lost

Useful link for travelers