1. Download your Facebook messenger history from your Facebook settings. More here.
2. Unzip your data into the directory of your choice.
3. Identify a person whose chat history you want to analyze.
4. Find the JSON file listing all of their messages with you (it's going to named after their username).
5. Now, run:

git clone https://github.com/dmhacker/facebook-message-analysis && cd facebook-message-analysis
python fbmsganalysis FILE

^{_{* Replace FILE with the path to the JSON file you identified earlier.}}

In a few seconds, you should have some nice & pretty graphs that might reveal some interesting insights and/or trends.

If you get an import error, it means that the dependencies that facebook-message-analysis needs are not installed.
Use this command inside the project directory to resolve this:

pip install -r requirements.txt

If you get an NLTK download error, it means that NLTK hasn't cached the stopwords file that facebook-message-analysis uses.
Use this command inside the project directory to resolve this:

python
>>> import nltk
>>> nltk.download('stopwords')
>>> quit()