Goa is mainly of 2 parts :- North Goa & South Goa
It depends on ur stay which is situated in either North Goa or South Goa. So accordingly u can plan for it. Suppose ur stay is in North Goa then u should first visit n cover all the site seeing places in South Goa n then u can cover places in North Goa
Goa is of two parts- North Goa south Goa. Since you are planning only for 4 days, either you plan North Goa exploration or south Goa exploration. If you are covering North Goa here are some spots you can cover in 4 days- starting with Vagator beach you can cover Baga, calangute, candolim, Arambol and sinquerium beaches. Forts like chapora, Reis magos fort are must visit spots. Anjuna flea market is a place to shop while try to plan one museum visit. The beaches mentioned above have water activities, in any of the beach you could enrol. Coming to south Goa- you could start with Palolem then move on towards, Arambol, colva and galgibaga beach. You could devote a day for dudhsagar falls which has some interesting activities around. Besides here beach shacks are popular while Tambdi surla temple and shri shantadurga temple are places to visit. You could also cover saviour word church and three kings church.
I'm 4 days of ur tour u can cover some of the places, Goa is divided in 2 districts, North goa and South goa, water sports, pubs, food and if u ra a party type guy, the u start from north goa, Baga, calungute, arjuna, vegator, panjim and mapusa are the most popular places to visit in North goa, in south goa u can cover madagon, vascodigama, colva, etc u can cover north goa by staying at baga or calungute, all places are under 15 kms radius only. if u plan to sout goa then it's better to stay in vascodigama and u can cover.
Places to visit in Goa:
Salim Ali Bird Sanctuary
Cabo De Rama
Reis Magos Fort
Savoi Plantation Goan backwaters
Butterfly Conservatory Happy journey 🙌
It depends on the kind of trip you have in your mind. If you want a peaceful trip then go to South Goa.You will be amazed by its beauty. You can visit Palolem, Arambol , butterfly and Cola beach (One of my favourite stay there for one at least one day).