Depends on How many days. The usual places are Baga beach, Calagute, chapora fort (Dil Chahta hai spot), Panjim, Candolim beach towards south.. there are plenty of options to choose from.
Day 1 arrival rentbike.in delivers bike at airport
day 2 stay at zostel calangute check out north goa vagator beach , fort , calangute beach, arambol beach, market , club and eatries in north goa
day 3 boat ride , and casino , chruch
day 4 go to south goa, checkout palolem beach , butterfly beach (must) , day5 dhudsagar waterfall