Before - seems to vary depending on where you're coming from and on your taste in ale. I don't know the area well enough to try to direct you. This subject was covered in some detail about this time last year so it may be worth a search if you've some time on your hands.

After - the Kings Arms directly under the East Stand is usually worth a try. Usually only have 'Smoothflow' which they try to pass of as ale, but by that time you're usually so depressed (surrounded by grinning Northerners) you're past caring...

Before the game lots in town, the Webb Ellis is a spoons where a lot of people go, or if the weathers nice walking from twickenham station turn left and walk down the high street to the river there is a pub called the Barmy arms on the river, if it's sunny it's a good place to go.
Cabbage patch is famous but a bit overpriced in my opinion, but so are most pubs round there tbh.
The stoop bars are open as soon as the turnstiles are, there might even be an U20s game on before the main match.

Afterwards under the east stand will have a band and should have a players award after.

Ireland

Thanks for the reply lads!
Good info there thanks for the responce!

According to the club there is a womens challenge match on before the main game

Might be more entertaining to watch this then leave.