I have travelled extensively alone and always had a ball!
European city break - I usually just book a flight and hotel/airbnb with no real plan, walk around and see the sights, try the local food and have a drink in the day. I went on airbnb experiences in one city and found someone doing a tour in English, I had a full day out sightseeing, all my pictures, food etc for about £40. In the evening I love going to somewhere really fancy and people watching. I find eating alone quite enjoyable, probably on the back of these trips.
European beach trip - Airbnb is so good for this! get somewhere with a kitchen and a shortish walk to the beach, then you can do your own breakfast/lunch. I stayed in one airbnb which had workaway staff, so ended up making friends with another Brit and we went off doing things for meals and days out with her work schedule allowing.
Further afield - I did Dubai alone by just booking hotels and flights and winging the rest because it is so westernised.
I went to India and booked through a tour company called Just You, ideal because it is for solo travellers who don't want to share a bedroom. I found the clientele were mainly all older than me, but we got on really well.
I hope you have a fab time wherever you go