Decorate without a central point and it becomes gaudy (6)
I believe the answer is:
garish
'gaudy' is the definition.
(I know that gaudy can be written as garish)
'decorate without a central point' is the wordplay.
'decorate' becomes 'gish' (I can't justify this - if you can you should give a lot more credence to this answer).
'without' means one lot of letters goes inside another ('without' can be similar in meaning to 'outside').
'a central' says to take the centre.
'point' becomes 'dart' (darts are pointed).
The central letters of 'dart' are 'ar'.
'gish' placed around 'ar' is 'GARISH'.
'and it becomes' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for garish that I've seen before include "Gaudy, excessively bright" , "Gaudy, over-decorated" , "Cheap, flash" , "Colourful in a vulgar manner" , "Tastelessly bright" .)