we sort of had a programme which we could have follow but it wasn't required. me and my mates didn't follow it, we were just on the beach and in discos, checking out girls and stuff, we weren't much for sight seeing. so i may not be able to help you out much, but from what i remember there were 2 things i ended up regretting.
marineland or aqualand, don't know how exactly it's called, it's one of the two for sure. anyway the name says it all, dolphin shows, numerous water falls, slides, supposedly it's great fun, even more if you're drunk. i can't tell you as i was drunk on the beach, i decided it's better to spend 20 euro on a few beers than some stupid swimming place. i was wrong, mistake nr.1
flaminco show, this i really regreted. you probably heard of it, anyway it's a local dancing, singing show. who ever went said not only is the show itself amazing, but the food and booze was just phenomenal and cheap. people came back aching, holding their stomachas cuz they got more than they can eat. waiters bringing you wine, sangria on the table constantly, you never have an empty plate at any time...it was really great and cheap as well, i think it was about 20, 30 euros. that was mistake nr.2
other than those two things i really don't know what else to say, everything in lloret is nightlife, beaches and stuff. in barcelona i was less than a day so i saw not much. nou camp is a must see, the bastards even charge the entrance 5 euro, even though there's no one playing. and the centre of barcelona is really pretty and a must see at night, when all the fountains are working, it's all really bright and amazing.
i'm sorry if i can't be of any more specific help, but i'm sure you'll understand, i was on my high school excursion. all i can tell you whatever you decide you won't miss out on lloret and barca that's for sure.