Group seen excitedly describing new mobile regularly ignored (8)
I believe the answer is:
ensemble
'group' is the definition.
(ensemble is a kind of group)
'seen excitedly describing new mobile regularly ignored' is the wordplay.
'excitedly' is an anagram indicator.
'describing' means one lot of letters goes inside another (describe can mean to form the outline of).
'regularly ignored' means one should take alternating letters.
'new'+'mobile'='newmobile'
The alternating letters of 'newmobile' are 'embl'.
'seen' anagrammed gives 'ense'.
'ense' going around 'embl' is 'ENSEMBLE'.
(Other definitions for ensemble that I've seen before include "Group of musicians playing together" , "Set of matches" , "Group of musicians or co-ordinated clothes" , "Musical group" , "Small group or complete costume" .)