Ok here goes....
well, clubwise I'd try a couple of the superclubs, welovesundays @ space is a must, starts at 8am sunday morning. people that havent gone straight from their friday night out tend to go mid afternoon and stay, well up to you, up to 6am. if you get to space before 4pm they give you a wrist band which allows you one pass out from the club. when you use this you can try another ibizan institution...
Bora bora, its a bar on the beach on playa den bossa that gets going at around 3pm, people dancing on the tables etc etc.
Also club wise I'd try a night at pacha, reputed as the worlds most beautiful club and I'd be inclined to agree. Subliminal is my favourite night there, house music from Erick Morillo.
Clubs are expensive, entrance ranges from £15-35 and drinks are on average around £6-10. so have a few drinks in some bars before hand and make use of the supermarlets for cheap booze.
Make sure you watch a sunset from cafe mambo or cafe del mar, again another chance to make use of the supermarkets, get cheap booze and sit on the rock outside the bars listening to the music. Friday is good as pete tong broadcasts live on radio 1 from cafe mambo.
If you after you average uk friday night out, bar crawl, drinks offers, lads you need to visit the went end. its here you will probably find old school music, there isnt a big club playing it this year as far as I know.
Try a night out in ibiza town, explore the old town and book a restaurant for a ncie meal. I like going to ibiza town when I am not clubbing and having a few drinks and doing a bit of shopping.
Restaurant wise there are hundreads of great places on the island, my favourite in san antonio is a mexican called tijuana. theres also another mexican called viva zapata which is really cheap but quite good.
For beaches I think san an is pretty limited, but 10 minutes in a taxi is cala bass and cala tarrida, both lovely. I'd avoid moped, far to dangerous IMO.
what you should do is use the search function on here and also read the review section.