I have had tapas a few times in London, with varying results. In particular, we had an amazing tapas experience while visiting Oxford last summer: fried goat's cheese with honey anyone?
But I've always associated tapas with the world of restaurants. Instead, Spain greeted me something completely different.
Tapas in Spain are usually served standing next to a bar that's coated end-to-end in uncooked food. You pay by the piece - ordering individual pieces of food as you feel like it, along with sangria, beer and wine. (Incidentally, this can make it very difficult to realise how much you've eaten - you just get in the habit of order, order, ordering).
In a popular tapas bar, you're usually crowded up to the walls:
|the bar is about as wide as this photo|
|caramel pudding on the bar|
We ended up sampling everything from the classics, to randomly pointing at things on the shelf - I don't think we had any misses! Part of this is because we ate quite a lot of tapas in San Sebastian - the culinary capital of the world, and home of tapas in Spain. The town is heaving with beautiful tapas bars (Lonely Planet dutifully guided us to some of the best).
I would recommend trying some of the classics - from patatas bravas (fried potatoes with spicy tomato sauce), to croquettes (soft potato and ham deep fried and crispy), to everything squid you can get your hands on, to cheese selection platters and the famous iberico ham. Iberico ham will cost you a small fortune, but it's one of those things worth paying for - the Spanish are rightfully obsessed with it!
Plus, at a proper tapas bar you can just point at whatever looks best in that moment. (The only way you'll be in trouble is if you're vegetarian. Then be prepared for....well, not much. In one or two places there were one or two options that appeared like they might be meat free - but vegetables doesn't seem to be something the Spanish are particularly concerned with).
So remember, when you go out for tapas in Spain:
1. Don't bother heading out until 9 or 10PM each night
2. Be prepared to stand all evening
3. Eat everything - ordering 1 or 2 pieces at a time by selecting items from the bar- along with a nice glass of Rioja wine or Sangria
4. Watch what you're eating - and spending - it can creep up on you unawares