Hi - I have passed all 3 associate level exams and found the Whizlab practice exams very useful, there werent any major gaps in coverage and they really spurred me on to go and understand why an answer was correct when I was in doubt. I did find the odd error but Whizlabs support responded quickly to anything i raised - thanks for your help.
I used a combination of:
a LOT of reading and re-reading AWS whitepapers
supplementing with additional info from the AWS ReInvent channel
and...most important of all extensive usage of the AWS platform itself, with as many labs as I could find.