Following on is straightforward (7)
I believe the answer is:
sincere
'straightforward' is the definition.
(I've seen this before)
'following on' is the wordplay.
'following' becomes 'since' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' becomes 're' ('on' can be mean 'with reference to').
'since'+'re'='SINCERE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for sincere that I've seen before include "Genuine; deceit-free" , "Lacking in deceit" , "Free from pretence" , "Free from deception" , "Candid" .)