As stated above, Cydia Substrate hasn’t been updated for iOS 8.3 yet, as Saurik wasn’t notified of the jailbreak release beforehand, so…you’ll have to wait a while before you can install some Cydia Substrate dependent tweaks.
I’d recommend waiting a few days before jumping the gun, as the jailbreak tool is still a little unstable, as users are reporting errors while trying to jailbreak, and having to downgrade iTunes for the jailbreak to successfully work, etc. On top of that Cydia Substrate isn’t updated neither are many jailbreak tweaks, anyway…
You can grab the TaiG jailbreak tool here [Windows]
Stay tuned as we work on a guide on how to jailbreak iOS 8.3
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