Well there's the ballot which started in August. And i've been quite fortunate - have been twice with the aid of the ballot tickets.
And i think official tickets come out maybe like a month before.
I dunno... i usually go early in the morning on the day or after school in the evening if there are any delayed matches - much cheaper!! That only really works for the first week though.
Second week - prices are high and it's hard to randomly get a ticket - that needs planning