London Xmas decorations/ shopping

[signtalker]

Were heading to London next Sunday
We live in the country and don't visit very often. Parking at shenfield and then catching the train to Liverpool Street, were only there for the day and wondered where is a good place to wander to see Christmas decorations and just walk around d shops( we've finished Xmas shopping)
Not high end designer but just to take in the festive time of the year, although I would like to visit Harrods just to look at their Xmas things.

Any do and don'ts tips?
Hubby is really good at getting around directions wise it's like haveing a sat nav with me

Any suggestions
Cheers
Jules