Read this (taken off a travel forum):
First of all, you can try the official website. Tickets go on sale approximately 2 weeks before match day, and you can be lucky and find seats this way. Alternatively, if you're already in town, you can make your way down to the ticket office at the stadium – with such a high capacity, it's rare for games to sell out – unless we're talking about the previous fixtures of Real Madrid or a semi final in the Champions League, of course! However, this information is readily available on the website or any affiliate program of Barcelona. What I'm going to reveal are the tricks.
Season ticket holders to FC Barcelona can only ever give their ticket back to the club, or maintain that ticket with the surname. So many older generation season ticket holders, simply hold on to their relatives' season tickets and sell on these seats on match day. Let me explain. Say my father and his 4 brothers were all season ticket holders, but of those 5 siblings, only 1 had children (me). I would renew those season tickets each year, due to their privileged location within the stands, and simply turn up 30 minutes before kick off each home game and sell on those tickets for face price, with the guarantee of having better view than the box office tickets and probably paying off my own season tickets from the profits by the end of the season. This is perfectly legal within the eyes of the club and the governing bodies of football, as long as money doesn't change hands. So those clever OAP's you see hanging around the metro station are the ones with the best tickets! The security guards at the turnstiles know the score, but as long as they haven't seen money changing hands, then its fine by them. This is the best way to get tickets for the match, as you are effectively escorted in by the seller (you will sit next to them), so no security risks with regards fake tickets. It does however, have its risks in that if anyone sees you pay for the ticket, then you run the risk of losing your money and the ticket.
Tickets for matches are released to the general public after the FC Barcelona Members can buy them. You pay an annual subscription to the club if you can't get a season ticket (based on my previous paragraph, you won't be surprised to hear that the waiting list for a season ticket extends back to the 1970`s) and then have first refusal for the tickets before the public. In this way, many "touts" will buy up their share of the ticket allocation, often meaning they take all of the second tier seats in the stadium or the second best seats, after the season ticket holders. They then have a mark up of around 5 Euros per ticket, which for the majority of tourists is a steal, considering the better seat you will be able to get for this first time experience.
My final tip is again, not one that is well publicised and although this means that you don't have the choice of the better seat allocation, it's an official way of going about getting a ticket. You may be surprised to hear that ATMs or cash machines of the bank "La Caixa" also sell FC Barcelona tickets. The Catalan bank sells concert tickets, opera entrances and theatre stalls, so it's no surprise to be able to find seats for the football, either. The reason why I left this tip for last is that due to the previous methods, the Cash point tickets are usually always the last to be sold, meaning you will have the cheapest seats (therefore be higher up in the stadium) which is not to put you off, as any seat in the stadium is well worth the price, but just so that you know you have various options. This option, for example, is great for larger groups who all want to stay together, as it means tickets can be bought in bulk – this way guaranteeing adjacent seating arrangements.
