there is a website which you can buy tickets before hand. it is
http://www.tauroentrada.com/ I have not used it but i do know that it was recommended to me when i worked in the tourist office in almeria. they do charge a little bit extra, but at least you have a ticket and is great if you are going in a large group so that you can all sit together. have fun, i was at one last week in Huercal Overa and it was great, a really good athmoshpere!