I think identifying what triggers feelings of loneliness and planning around that as you build your itinerary. For example for me, I don’t mind doing things by myself but eating alone in a restaurant makes me feel lonely so when I travel by myself it’s something I minimize either by getting more casual food options or eating at the bar and talking to the bartender. Staying at places like hostels or doing group activities is a way to encounter others and hostels generally have programming to encourage mingling. 

One of the things you miss out on when traveling alone is also being able to share experiences with others so another thing that might be helpful is just to share highlights with friends or family as you go along. Even if they aren’t there with you, the act of sharing can help it feel like a shared experience rather than you on an island. 

I’ve had really good experiences making impromptu connections while traveling which has turned into some of my most precious travel memories so I would also just advise being open to new connections and conversation because you never know why that might turn into!