Parsing is a great tool for monitoring and improving your DPS, DTPS, HPS, and Threat generation.
The first thing you need to do is enable combat logging in game. Go to Preferences, then Combat Logging. Make sure Enable Combat Logging to File has a filled box next to it.
Next, make sure you are able to find where your computer is storing this data. You may need to enter combat after enabling this in game so the folder and files will be created. This is where the files are stored on my computer, but it may be different depending on how your game and storage is set up.
There are two great free tools that analyze and interpret these combat logs for us: StarParse and Parsely. You can use either or both of these. They both serve their own purpose and are useful in different ways.
StarParse is great to use in game, giving immediate feedback as you are fighting via its game overlay system.
Parsely is great for sharing and comparing parses (between yourself and others) and analyzing the rotations, GCDs, etc. after fighting of yourself or the top players!
StarParse can be downloaded from this website: http://ixparse.com/.
Here is a great guide for installing, setting up, and using StarParse: https://youtu.be/_-vdNiNwdeY.
The trickiest part (in my opinion) of setting up StarParse is making sure it knows where to find your combat logs, which it could not find when I first set mine up. In StarParse, go to File: Settings and on that very first setting page, it gives you the option for choosing where to pull combat logs from. The file path should match that from the one we found previously.
In game, you can customize your overlays to show as much or as little detail as you want. You can move the overlays around, change which datums you see, and so much more! This is what my overlay normally looks like:
Parsely is entirely online, and is located here: https://parsely.io/.
To use Parsley, simply create an online account. To upload a parse, simply use the Select Combat Log and find the relevant file and hit Analyze. You can select a guild (keep reading to see how to do this), add a note/description, and change the visibility settings. Public parses become available on the website's leaderboards.
Once the file is uploaded, Parsely will analyze the data and automatically redirect you to a page that has tons of information and analysis features. It should look something like this:
One of the cool features of Parsely is that you can associate with a guild and even have guild raid leaderboards. The first picture shows you a generic dummy-parse leaderboard, which includes players' guild names. The second shows you a raid leaderboard for specific fights (with an awesome guild at the top!!!)
To be able to upload your parses under a guild's name, click on the Guilds tab and copy the given code to give to your leadership, or whoever has access to your guild's Parsely account. Then, you can add a guild to any parse, or even add a guild to a parse you had previously uploaded!