Two weeks for a solo first trip? My first thought is ... try a bit of everything while you have the chance. If you go back later with friends, you'll probably have to compromise a lot, and it's a lot harder with a group to try something new and then feel free to leave in an hour if you don't like it.
Most of my trips have been solo, and the things that have meant the most are the experiences and connections that seem unique to Ibiza. So ...
Give yourself an afternoon to wander up the streets, buildings and such of the old Dalt Vila in Ibiza town, with amazing views from the top.
Spend an evening partying under the landing planes and olive trees of DC10 for Circoloco
Check out at least one night of music that's outside what you'd usually go to see
Stay out late at one of the big clubs until closing at dawn, so you can watch the sun rise on the way back to your hotel
Be open to meeting and talking to people, and to joining them for a bit of adventure if asked (within reason)
... and that last one most of all. Those times can be life changing, for the better -- they sure have been for me