In terms of a tutorial, I'm unsure if anyone has done one online, probably because of growing interest in Cross-Development Languages, I think Sean McManus'
The BASIC Idea maybe the closest thing
Amstrad did make a BASIC tutorial guide and Parts
One &
Two are available on CPC-POWER with Manuals in PDF format.
Personally I typed in a number of BASIC examples from a Tutorial Amstrad Computer User had in 1991, which I thought was quite good despite being badly presented with examples presented in a non-fixed typeface, that series is also on CPC-Power as
Parts 1 to 7 with JPG scans of that Tutorial series!
Apart from that a number of my threads on here may help, in
Study of 464 Only Game Helicopter/Destination Saturn from ACU, I dismantle each level from that game into individual games.
In
My BASIC Simple Platform Game w/ Alternative Sprite Drivers, I took a simple Platform game I coded and enhanced with Sprite Drivers which could be used from BASIC.