Following lead, maybe at intervals fairly simple? (10)
I believe the answer is:
elementary
'simple?' is the definition.
(I know that simple can be written as elementary)
'following lead maybe at intervals fairly' is the wordplay.
'following lead maybe' becomes 'element' (I can't explain this - if you can you should give a lot more credence to this answer).
'at intervals' indicates alternate letters (letters are taken at regular intervals).
The alternating letters of 'fairly' are 'ary'.
'element'+'ary'='ELEMENTARY'
Can you help me to learn more?
(Other definitions for elementary that I've seen before include "Simple, my dear Watson!" , "Primary" , "description of subatomic particle" , "Rudimentary; introductory" , "ABC!" .)