Because people are ALWAYS asking, I decided to make this helpful guide.
Step 1. Download
To fly, you will need WoM client. The most recent version of the program can always be found at http://t9k.me/y6 . Go to the side of the page, and sign up.
Step 2. Unzip
If you don't already have a extraction program, install 7-Zip found at http://t9k.me/y7 . Right click the file you got from world of minecraft, and go to 7-zip -> extract files. Navigate to the folder you extracted the files to.
Step 3. PLAY!
Run wom.exe. You are done! Type in your username and password and click sign in. Select the server you wish to join, then click go. Just a run down of the keys:
Z toggles flight.
Hold down X while moving to pass through walls.
Q is to go up,
E is to go down.
Shift boosts your speed by 5x,
Control boosts your speed by 2.5x.
That's all there is to it! If you have any questions (and this guide is so simple, I couldn't imagine you having one) leave them in the comments section