I know there are other ways of doing this, but if your a licensed iOS Developer you can simply sign the code in your App and put it on to one of your registered testing Devices that's jailbroken and follow the step by step instructions below:
Download iFile from the Cydia Store. I would suggest paying for it, but you can find other sources where you can get a cracked version. Then use iFile on the device and go into the following directory:
var/mobile/Applications/YourAppName
Select YourAppName.app folder
Tap the zip file button, (between + and trash buttons at bottom of display)
You will be prompted to name the zip file and hit create.
That's the zip file you submit to Cydia, you can email it to yourself from within iFile, or if you want use a program like DiskAid to pull it from your Device. DONE!
TESTING
To test you need to copy the .app file into the following directory:
var/stash/Applications
Exit iFile and Delete your app from the devise. Respring, Reboot, or Restart.
The icon will then be on your desktop.
HOPE THIS HELPS SOMEONE!!!
Note: This is against Apple policy, but if you don't tell I won't ;)