Learn z80 ASM in 28 days is, as far as I know, the only complete ASM guide. However, the CE uses
ez80 ASM which is very similar to regular z80. So the guide may still be useful to you. There are definitely differences, so I'd suggest browsing the forum for others who tried to learn ez80 ASM. I'd also suggest looking at ASM projects that are open source. I.E. 'Attack of the Snails' or 'Cesium'.
Before you attack ASM programming I'd highly suggest you expand your skills with C (using the resources Jeffitus posted above), or easier, BASIC. A great resource for BASIC is
TI Basic Developer; it's an amazing resource and I still use it, even 3 years after starting BASIC. Getting a good foundation in BASIC makes it much easier to learn other languages. Starting your programming experience straight into ASM is possible, but it's going to hurt and wont be very fun. Many of us here wanted to go right into ASM but I don't know anyone of us that succeeded (except maybe Kerm) without learning another language first.
Welcome to Cemetech, good luck learning ASM.