Obviously, your iDevice should be jailbroken for this. You will also need OpenSSH installed, or have USB access to your root folders. For this tutorial, I am using iPhone Disk, which is free right now for Mac and Windows. You will also need a simple text editing tool. I will be using Text Wrangler.
Access your root file system, and navigate to Applications/Cydia.app. Right click on Cydia.app and select Show Package Contents. (If you are using SSH for access, you will not need to show package contents).
Now, navigate to package.js. Save a back up of this file to your desktop, just in case you mess something up. Open the original file with your text editor of choice.
Now look for the line of code you see in the screen shot. It is at around line 198. Change the line of code from if (depiction == null) to if (depiction == null || true). Save the file, and reboot your device.
Now, when you open Cydia, you should notice a huge speed difference. This may not change the initial start up of Cydia, but rather, the time it takes to load packages when you select them. Try it for yourself and see if you notice the difference. Comment below, with your experience.