Usually, I would switch to a French keyboard layout when I have to type some text in French. It's to quickly access the accented characters. In the GNOME desktop environment it is straight forward to add multiple keyboard layouts. Typically, I would have English-US, French-FR and Hindi-IN/Bolnagri layouts.
A few days ago, a colleague of mine noticed me switching the layout and showed me it's instead better and simpler using the Alt Gr key. Also known as the AltGraph key, this button comes very handy to type accented characters such as é, à, ç, ï, etc.
In GNOME 3, follow Settings > Keyboard > Input Sources and replace the English (US) layout by English (international AltGr dead keys) layout.
Now, accented characters can be typed as follows:
Alt Gr + ' + e = é
Alt Gr + ` + a = à
Alt Gr + " + i = ï
Alt Gr + , + c = ç
More about the Alt Gr key on Wikipedia.