Barcelona in November - Buy tickets ahead for trains/sites?

Brenda, there's no high or low season in Barcelona. Besides the fact the city receives tourists all year round, hotel and restaurant availability -as well as access to tourist sites- is governed by the events happening in the city, not by the time of the year. So, in general, it's best to pre-book all the tickets to the most popular sites/attractions. As per train tickets, note that commuting and regional trains can't be pre-booked, one buys the ticket on the day. For high speed and long distance trains, one can pre-book online and for some journeys it's best to do so in advance.

I'd definitely buy a (timed) ticket for La Sagrada Familia ahead of time, rather than just showing up, even in November. The conventional wisdom says that it's best to try for the first time slot on your preferred date so you can enjoy some uncrowded time in the church. Be aware that access to one of the towers (your choice) requires a separate timed ticket. The tourist office will sell you the basic ticket for LSF for a 2-euro service fee but does not handle the tower tickets. At least for summer travelers, advance purchase (one day ahead often being sufficient) is also advised for Parc Güell, Casa Batlló and La Pedrera/Casa Milà. All those tickets can be obtained from the tourist office, again for a fee of 2 euros per ticket.

I was in Barcelona last week and we purchased our tickets for La Sagrada Familia and the Nativity tower on line the night before, just to be safe. We went on a Monday, and when we arrived around 1 pm, they still had tickets available from 2:30 pm on.

Many trains run to/from Valencia, with no deadline to purchase. On the fastest departures, booking a Promo fare 1-2 weeks out saves about 10-15 euros each way, per person at www.renfe.es, but tickets are nonrefundable and nonchangeable. The savings is not necessarily worth the tradeoff in flexibility. Booking roundtrip can also earn a discount. If using Renfe online, pay with PayPal, since international credit card approval is often an issue on that site.

Thank you all for your help! I think we should play it safe and get our tickets
in advance for the most popular sites.

My first time using this forum and it is great!

I just returned from Barcelona this week.
I went to the Sagrada Famillia without a timed ticket thinking "It's November ..."
There wasn't a line at the ticket booth, but the next timed entry was 2 full hours later!
That gave me lots of time to study the exterior and get a coffee in the park across the street ...
People were ordering their tickets on line and then just showing the e-ticket from their phones or tablets, so you could probably do it the night or morning before and not need to worry about printing.
You have to buy your audio guide and tower ticket all at the same time. I didn't know this so missed out on both, but my visit was great anyway.
It wasn't crowded inside, which was nice. And the interior space is gorgeous!
Enjoy!
SharYn

Thank you SharYn!